This primarily implements DecorationImage.lerp().

It also makes some minor tweaks, the main one of which is defering to dart:ui for `clampDouble` instead of duplicating it in package:foundation.

Fixes https://github.com/flutter/flutter/issues/12452

This was first landed in https://github.com/flutter/flutter/pull/130533 and reverted in https://github.com/flutter/flutter/pull/131347.

Reverts flutter/flutter#130533

Tree breakage.

This primarily implements DecorationImage.lerp().

It also makes some minor tweaks, the main one of which is defering to dart:ui for `clampDouble` instead of duplicating it in package:foundation.

Fixes https://github.com/flutter/flutter/issues/12452

## FlutterTimeline

Add a new class `FlutterTimeline` that's a drop-in replacement for `Timeline` from `dart:developer`. In addition to forwarding invocations of `startSync`, `finishSync`, `timeSync`, and `instantSync` to `dart:developer`, provides the following extra methods that make is easy to collect timings for code blocks on a frame-by-frame basis:

* `debugCollect()` - aggregates timings since the last reset, or since the app launched.
* `debugReset()` - forgets all data collected since the previous reset, or since the app launched. This allows clearing data from previous frames so timings can be attributed to the current frame.
* `now` - this was enhanced so that it works on the web by calling `window.performance.now` (in `Timeline` this is a noop in Dart web compilers).
* `collectionEnabled` - a field that controls whether `FlutterTimeline` stores timings in memory. By default this is disabled to avoid unexpected overhead (although the class is designed for minimal and predictable overhead). Specific benchmarks can enable collection to report to Skia Perf.

## Semantics benchmarks

Add `BenchMaterial3Semantics` that benchmarks the cost of semantics when constructing a screen full of Material 3 widgets from nothing. It is expected that semantics will have non-trivial cost in this case, but we should strive to keep it much lower than the rendering cost. This is the case already. This benchmark shows that the cost of semantics is <10%.

Add `BenchMaterial3ScrollSemantics` that benchmarks the cost of scrolling a previously constructed screen full of Material 3 widgets. The expectation should be that semantics will have trivial cost, since we're just shifting some widgets around. As of today, the numbers are not great, with semantics taking >50% of frame time, which is what prompted this PR in the first place. As we optimize this, we want to see this number improve.

* isCanvasKit implement and test

* isCanvasKit implement and test

* ++

* forgot license

* make isCanvasKit a getter

* addressed comments

* forgot to change names of integration test files

* typo

* simplified tests

* comments

* Use persistent hash map to store _inheritedWidgets

Instead of using a HashMap and copying it down the tree
which leads to quadratic time and space complexity
use a persistent data structure which can amortize
the cost by sharing parts of the structure.

The data shows HAMT based PersistentHashMap to be
5-10x faster for building _inheritedWidgets and
considerably more space effecient (e.g. bringing
amount of memory allocated when constructing
_inheritedWidgets in a tree with 150 InheritedWidget
down to 70Kb from 970Kb).

PersistentHashMap is slower than HashMap for
access: 2-3x in relative terms, but in absolute
terms we are only talking about ~0.2ns slow down
per access and various app benchmarks we run have
have not revealed any significant regressions.

* migrate foundation to nullsafety

* address review comments

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This reverts commit 90500a5d.

Before this, we had several places where an isReleaseMode was defined, all with the same definition. This just makes it more broadly visible to allow our users to use it, as well as creating debug and profile versions, and adding a device lab test for it.

Since this is a const value, this makes it possible for a developer to easily mark blocks that can be removed at AOT compile time.

* use HttpOverrides and dart:io HttpClient in flutter

* add missing package:http dependency

* update flutter packages and remove comment about createHttpClient from flutter_test

* move byte loading logic to common class, move string parsing logic to base class

* addAll doesn't work for a Uint8List

* use bytes.setRange

* undo addition to hello_world

* add newline to end of binding.dart

* and a newline for hello world

* refactor to function and add tests

* address comments on unknown length case

* alignment

* sort alaphabetically

* rename convertResponse to consolidateClientHttpClientResponseBytes.  Add header

* fix alignment in test

* Move the splitting of licenses to an isolate

This improves (from horrific to terrible) the performance of the
license screen. It also introduces a feature in the foundation layer
to make using isolates for one-off computations easier.

The real problem that remains with this, though, is that transfering
data between isolates is a stop-the-world operation and can take an
absurd amount of time (far more than a few milliseconds), so we still
skip frames.

More work thus remains to be done.

* - Add profile instrumentation to the isolate compute() method
- Add profile instrumentation to the LicensePage
- Add profile instrumentation to the scheduleTask method
- Make scheduleTask support returning a value
- Make the license page builder logic use scheduled tasks so that it doesn't blow the frame budget

Summary:

- Add `key` field to `SemanticsNode`, while moving key into `foundation` library so it can be used by the render layer.
- Introduce `SemanticsProperties` and move many of the `Semantics` fields into it.
- Introduce `CustomPaintSemantics` - a `SemanticsNode` prototype created by `CustomPainter`.
- Introduce `semanticsBuilder` and `shouldRebuildSemantics` in `CustomerPainter`

**Breaking change**

The default `Semantics` constructor becomes non-const (due to https://github.com/dart-lang/sdk/issues/20962). However, a new `const Semantics.fromProperties` is added that still allowed creating constant `Semantics` widgets ([mailing list announcement](https://groups.google.com/forum/#!topic/flutter-dev/KQXBl2_1sws)).

Fixes https://github.com/flutter/flutter/issues/11791
Fixes https://github.com/flutter/flutter/issues/1666

(in preparation for moving the semantics stuff out of rendering)

Add Diagnosticable base class and documentation

* add a profile() method

* add todos

This reverts commit 4b4cabb7.

* fire service protocol extension events for frames

* start time in micros

* introduce a profile() function; only send frame events when in profile (or debug) modes

* moved the profile() function to foundation/profile.dart

* refactor to make the change more testable; test the change

* fire service protocol events by listening to onFrameInfo

* remove the frame event stream; add a devicelab test

* remove a todo

* final

It was 8.0. It's now arbitrarily 18.0.

Changing this required adjusting some tests. Adjusting the tests
required debugging the tests. Debugging the tests required some tools
to help debugging gesture recognizers and gesture arenas, so I added
some. It also required updating some toString() methods which resulted
in some changes to the tree diagnostics logic.

Also I cleaned up some docs while I was at it.

Mainly, this adds documentation to members that were previously
lacking documentation.

It also adds a big block of documentation about improving performance
of widgets.

This also removes some references to package:collection and adds
global setEquals and listEquals methods in foundation that we can use.
(setEquals in particular should be much faster than the
package:collection equivalent, though both should be faster as they
avoid allocating new objects.) All remaining references now qualify
the import so we know what our remaining dependencies are.

Also lots of code reordering in Flutter driver to make the code
consistent and apply the style guide more thoroughly.

And add a test to verify we don't do this again.

There are more places we can use this annotation, but this patch just gets us
started.