* more const immutable classes

* more const constructors in dev/ and examples/

Use `curly_braces_in_flow_control_structures` for `foundation`, `gestures`, `painting`, `physics` (#104610)

* Use `curly_braces_in_flow_control_structures` for `foundation`

* Use `curly_braces_in_flow_control_structures` for `gestures`

* Use `curly_braces_in_flow_control_structures` for `painting`

* Use `curly_braces_in_flow_control_structures` for `physics`

* fix comments

* remove trailing space

* fix TODO style

* migrates lib/foundation and lib/widgets

* migrates lib/painting and lib/material

* migrates lib/cupertino, lib/gestures, lib/services, lib/semantics and lib/rendering

* fixes failing tests

* migrates test/

* improves hashing of lists

* Call image stream listeners with new flag

* Make _synchronousCall private

* Rename _synchronousCall parameter to be more descriptive and add more documentation

* Rename _hasInitialListeners to _addingInitialListeners and provide a better explanation

* Formatting fix

* Add tests

* Remove dependency on decoration_test.dart

* Simplify tests

* Remove empty line in comment

* Documentation

* Trigger tests

* Trigger tests

* Flip boolean value

* Remove chunk event subscription when disposing a MultiFrameImageStreamCompleter

* Add impl..

* stray prints

This reverts commit 5fd259be.

This adds a smoke test for every single API example. It also fixes 17 tests that had bugs in them, or were otherwise broken, and even fixes one actual bug in the framework, and one limitation in the framework.

The bug in the framework is that NetworkImage's _loadAsync method had await response.drain<List<int>>();, but if the response is null, it will throw a cryptic exception saying that Null can't be assigned to List<int>. The fix was just to use await response.drain<void>(); instead.

The limitation is that RelativePositionedTransition takes an Animation<Rect> rect parameter, and if you want to use a RectTween with it, the value emitted there is Rect?, and one of the examples was just casting from Animation<Rect> to Animation<Rect?>, which is invalid, so I modified RelativePositionedTransition to take a Rect? and just use Rect.zero if the rect is null.

* Add missing parameters to DecorationImage

* tune docs

* fix test