Rewrote CupertinoAlertDialog to look nearly identical to an alert dialog in iOS. This includes considerations for blur, translucent white background color, button sizing, gap dividers between buttons, and text scaling layout behavior. (#18381)

Adding CupertinoActionSheet, showCupertinoModalPopup

This fixes https://github.com/flutter/flutter/issues/18057

See details in our proposal for this breaking API change and #18057. This PR setup all code paths to allow the change but doesn't change the clip behavior by itself. We'll change `defaultClipBehavior` from `Clip.antiAlias` to `Clip.none` in the following PR to change the clip behavior and update tests.

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

This should fix #18952 and #813

Move the notch computation from the FAB to the BAB.

The notch in the BAB (bottom action bar) for the FAB (floating action button) was previously kept as part of the FAB's implementation. This was done to keep the shape of the FAB and the shape of the notch coupled.
That approach resulted in a somewhat complex and 'non Fluttery' mechanism for propagating the notch computation from the FAB to the BAB.

This CL uncouples the FAB and the notch computation.
With the new API the BAB computes its overall shape including the notch using a NotchedShape delegate.

This includes multiple breaking changes:
  * Scaffold.setFloatingActionButtonNotchFor is deleted.
  * The ComputeNotch type is deleted.
  * The hasNotch property of BottomAppBar is deleted.
  * The notchMargin property of FloatingActionButton is deleted.

Quick migration guide from the previous API:

| Previous API | New API |
| ------------------|-------------|
| BottomAppBar(hasNotch: false) | BottomAppBar() |
| Using a FloatingActionButton with: BottomAppBar() / BottomAppBar(hasNotch: true) | BottomAppBar(shape: CircularNotchedRectangle()) |
| Scaffold.setFloatingActionButtonNotchFor(..) | No longer supported |

* update tests for TextStyle changes in engine

* roll engine, support Foreground on TextStyle

* roll to TextStyle.foreground

* add tests, update docs, fixes from tests

* add golden tests

* stroke + gradient

* update goldens hash

* Use centered widget

* fix typo

* Disable golden tests until Linux generated files are available

* update goldens

This adds an HSLColor class which uses a perceptual color space based upon human perception of colored light (as opposed to HSV, which is based on pigment colors).

You can see the difference in the color spaces here: https://en.wikipedia.org/wiki/HSL_and_HSV

I also added a "within" matcher for both HSLColor and HSVColor that will check if the (floating point) color components are within a certain error.

And tests.

fuchsia_tester.dart still assumes Dart 1. Previously, it ran tests directly
from source, flutter_platform.dart automatically runs a kernel compile when
operating in Dart 2 mode, but this assumes a functional Dart SDK is available
in the artifacts directly, and fuchsia_tester.dart mocks out the artifacts
directory with an empty temp dir.

Remaining work is:
1. Get the frontend server building as a dependency on Fuchsia.
2. Patch fuchsia_tester.dart to use a valid Dart SDK and frontend server.

This also reverts migration to Dart 2 typedef syntax.

This reverts commit 6c56bb24. (#18362)
This reverts commit 3daebd05. (#18316)

Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.

Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.

No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.

* Expose Gradient.radial

* cleanup doc

* update tests, null check

* add asset images

This PR adds a SweepGradient class, extending Gradient to expose the engine's ui.Gradient.sweep shader.

Similar to LinearGradient and RadialGradient - SweepGradients can be used in a BoxDecoration or passed to a Paint's shader.

Revert "Update typedef syntax to use Function notation and turn on lint for old notation. (#18035)" (#18041)

This reverts commit 32586020.

Fixes #18028

Just changes typedef declarations, no logic changes.

I'm moving the assets in the assets-for-api-docs repo to a slightly different location to help with organization in that repo, so this PR points the doc URLs to the new location. The old assets won't be removed until this PR makes its way to the API docs website.

No documentation or code changes here, other than changing doc image URLs.

See https://github.com/flutter/flutter/issues/11961