This widget matches the style of the iOS slider widget. We don't yet
have the proper visual design for the disabled state.

Fixes #7252

This patch makes the CupertinoSwitch follow the style of the iOS switch
more accurately.

This patch contains a first draft of an iOS-style switch. We'll likely need to
tweak the constants upon closer study, but the basics are here.

Dart will parse this path as a URI, and multiple leading slashes will cause
that part of the path to be parsed as an authority.

Fixes https://github.com/flutter/flutter/issues/7279

Also see https://github.com/dart-lang/sdk/issues/28143

* rename DestinationLabel and labels properties to BottomNavigationBarItem and items

* update/fix comments

* grammatical changes

* add myself to AUTHORS

Port DecelerateInterpolator to Flutter.

Also, hide the Curve subclasses that you can't extend and that have no
statics and are generally not useful.

Callers can manually validate by calling validate(), or tell the Form to
validate on every change by setting the `autovalidate` parameter.

Fixes https://github.com/flutter/flutter/issues/7219

* Update CONTRIBUTING doc to mention analysis

* Update CONTRIBUTING.md

- [x] Introduce DependencyChecker which can determine if any dependencies have been modified.
- [x] Move the DartDependencyBuilder into a separate file.
- [x] Add unit tests for DartDependencyBuilder.
- [x] Add unit tets for DependencyChecker

Part of #7014 

Sometimes you have several listenables, but you want to hand them to an
API (e.g. CustomPainter) that only expects one.

* Animate size of label text over text fields.

Also fade in the hintText so it doesn't pop in immediately as the label
text slides up.

Fixes https://github.com/flutter/flutter/issues/7217

* rm annotations

* test

* rename

Without this, an FLX with no assets may be completely empty in AOT mode.
This will result in a warning when the engine's unzip library tries to
parse the FLX.

Fixes https://github.com/flutter/flutter/issues/7060

See https://github.com/flutter/flutter/issues/7248

Fixes https://github.com/flutter/flutter/issues/7017

Fixes https://github.com/flutter/flutter/issues/6943

Fix _DragAvatar to display in the proper position for Overlays whose Point.origin is not the global Point.origin. (#7223)