This normalizes all of the "See also" blocks in comments so that they conform in style.

They all look like this now:

  /// See also:
  ///
  ///  * [MyFavoriteWidget], because it's cool.
  class Foo {}

I removed some useless "See also" blocks, and added commentary to ones that were just "bare" references.

This is my penance for adding so many bullets that are "-" instead of "*". :-)

* implicit-casts:false in flutter/lib/src/rendering

* address review comments

* 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 PR adds TargetPlatform.macOS to the TargetPlatform enum. This allows us to begin implementation of some adaptive UI based on which target platform is desired.

I haven't updated the tests here, that will come in a follow-up PR.

* Replace hard break of Layer.find/All with findAllAnnotations
* Deprecate findAll

* Adds a new parameter bool opaque to MouseRegion
* The same to RenderMouseRegion and AnnotatedRegionLayer
* Add findAnnotations to Layer 

Teach Layer and its implementations, RenderObject and its implementations, and PaintingContext to reuse engine layers. The idea is that a concrete RenderObject creates a Layer and holds on to it as long as it needs it (i.e. when it is composited, and the layer type does not change). In return, each Layer object holds on to an EngineLayer and reports it to the engine via addRetained and oldLayer. This allows the Web engine to reuse DOM elements across frames. Without it, each frame drops all previously rendered HTML and regenerates it from scratch.

For #21756

For retained rendering, we don't want to push the offset down to each leaf layer. Otherwise, changing an offset layer on the very high level could cascade the change to too many leaves, which means that we can't retain them.

To not push the offset downwards, we simply push a TransformLayer when there's an offset. Skia has a fast path for concatenating scale/translation-only matrix so this operation should be fast (no performance regression is measured on Moto G4).

This is our first step towards https://github.com/flutter/flutter/issues/21756

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

Fixes https://github.com/flutter/flutter/issues/18971

It should account for the device pixel ratio

https://github.com/flutter/flutter/issues/16859

Orientation, and by extension time for rotation between orientations,
was aspirational and never used.

While this is technically a breaking change, this code never actually
did anything. If you were setting either orientation or timeForRotation,
simply delete those parameters and the code will continue to behave
identically to how it had been.

These properties had a high cost in the documentation because they're
all top-level properties, and there's really very little reason for
these values to be configurable in the first place.

Add Diagnosticable base class and documentation

Refactor RenderObject.toStringDeep and Widget.toStringDeep code to use DiagnosticsNode.

Previously we used logical pixels. This made the accessibility metrics
tiny on modern devices, since the OS works in physical units.

Also add a bit more debugging info and some docs.

Turns out we have many immutable classes.

Fixes #6892

* Manually fix every use of Point.x and Point.y

Some of these were moved to dx/dy, but not all.

* Manually convert uses of the old gradient API

* Remove old reference to Point.

* Mechanical changes

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\bPoint[.]origin\b/Offset.zero/g'
git ls-files -z | xargs -0 sed -i 's/\bPoint[.]lerp\b/Offset.lerp/g'
git ls-files -z | xargs -0 sed -i 's/\bnew Point\b/new Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bconst Point\b/const Offset/g'
git ls-files -z | xargs -0 sed -i 's/\bstatic Point /static Offset /g'
git ls-files -z | xargs -0 sed -i 's/\bfinal Point /final Offset /g'
git ls-files -z | xargs -0 sed -i 's/^\( *\)Point /\1Offset /g'
git ls-files -z | xargs -0 sed -i 's/ui[.]Point\b/ui.Offset/g'
git ls-files -z | xargs -0 sed -i 's/(Point\b/(Offset/g'
git ls-files -z | xargs -0 sed -i 's/\([[{,]\) Point\b/\1 Offset/g'
git ls-files -z | xargs -0 sed -i 's/@required Point\b/@required Offset/g'
git ls-files -z | xargs -0 sed -i 's/<Point>/<Offset>/g'
git ls-files -z | xargs -0 sed -i 's/[.]toOffset()//g'
git ls-files -z | xargs -0 sed -i 's/[.]toPoint()//g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point, /show /g'
git ls-files -z | xargs -0 sed -i 's/\bshow Point;/show Offset;/g'

* Mechanical changes - dartdocs

I applied the following at the root of the Flutter repository:

git ls-files -z | xargs -0 sed -i 's/\ba \[Point\]/an [Offset]/g'
git ls-files -z | xargs -0 sed -i 's/\[Point\]/[Offset]/g'

* Further improvements and a test

* Fix minor errors from rebasing...

* Roll engine

Fixes #4301

Covers lib/ in package:flutter.

I've been using these locally, but they're likely to be useful to other people
as well.