This patch fixes a collection of issues with widgets involved in text
editing:

  * Fire widget.onChanged on EditableText value change:
    The value of an EditableText is composed of the text value as well
    as other editing-related data such as selection-related information.

    Previously, widget.onChanged() was only called for updates via
    updateEditingValue(). For pastes via a TextSelectionOverlay, updates
    are signalled via _handleSelectionOverlayChanged(), which only ever
    triggered widget.onSelectionChanged(), but not widget.onChanged().

    Both updateEditingValue() and _handleSelectionOverlayChanged()
    perform the value update via _formatAndSetValue(), which is where
    this patch moves the widget.onChanged() call.

  * Correctly update TextFormField value on edits via controller:
    The textual value of a TextFormField exists in two locations:
      1. FormField.value, as with all FormFields and subclasses.
      2. TextEditingController.value associated with the TextField
         underlying the TextFormField.

    Previously, edits to the TextEditingController associated with a
    TextFormField resulted in updates to the rendered TextField widget,
    but did not update TextFormField.value. FormField.value is updated
    via FormField's onChanged function, which is called from the
    EditableText underlying the TextField underlying the TextFormField.
    EditableText only fires onChanged when it receives changes from the
    engine. It does not fire onChanged for changes made to the
    underlying TextController, since the owner of the TextController is
    the one making these changes and thus, already aware of them.
    FormField, however, *does* need to listen to these changes to update
    its value.

  * Adds an initialValue parameter to the TextFormField constructor:
    FormField's constructor already takes an initialValue parameter,
    which specifies the initial value in the field, which is also the
    value to which reset() returns the field.

    Previously, TextFormField took its initial value from the controller
    value (if a controller was passed in) or the empty string (if not).
    This had the undesirable effect that calling reset() always resets
    the value to the current value of the controller... i.e., does
    nothing.

    We now take an initial value explicitly.

* SafeArea

* AnimatedSafeArea

* AppBar test

* Apply feedback

* Update AUTHORS

* Add background and value colors to LinearProgressIndicator

* Add tests for LinearProgressIndicator with colors

Differentiate between 'not installed' and 'not working' and emit a more
targeted message.

* Clone hot reload benchmark for --preview-dart-2 option.

* Get rid of linux and win preview_dart_2 (only android would be sufficient for now). Refactor code into lib/tasks

* Revert 2016 to 2017

* Mark new test as flaky

Adds a test that verifies that EditableText sends a
TextInput.setEditingState message to the engine when the associated
TextEditingController is replaced.

This class lives in the Context and allows callers to "inject"
flag values, where flag values are first extracted from the
command arguments, then from the global arguments as a fallback.

Add multiline keyboard support to editable text widget.  Fixes #8028.

* Send scroll progress with ScrollCompletedSemanticsEvent

This requires engine change https://github.com/flutter/engine/pull/4144

* fix analyze warning

* review comment

* Roll engine to 45b11f742d38ebf564a5a832b1af00661d1a31fa

* fix test

Rolling the engine so I can land the flutter side of multiline text changes.

There are no other changes since the last roll.

* Update engine.version

Rolls engine to have:
* https://github.com/flutter/engine/pull/4139 Replace a View.getDisplay call that is not supported on API level 16 
* https://github.com/flutter/engine/pull/4135 Remove spurious error message
* https://github.com/flutter/engine/pull/4141 Clamp overflows in Color.lerp
* https://github.com/flutter/engine/pull/4125 Update vulkan semaphore extension

* Update engine.version

* Seems like a lint was renamed.

Lint `- unnecessary_brace_in_string_interp` is not in the list here: http://dart-lang.github.io/linter/lints/

In linter [0.1.30](https://github.com/dart-lang/linter/blob/9652dd44b6b32d5c8fc0262f67e037842ef207cc/CHANGELOG.md#0130): [http://dart-lang.github.io/linter/lints/unnecessary_brace_in_string_interp.html](unnecessary_brace_in_string_interp)
In linter [0.1.2](https://github.com/dart-lang/linter/blob/9652dd44b6b32d5c8fc0262f67e037842ef207cc/CHANGELOG.md#012): [http://dart-lang.github.io/linter/lints/unnecessary_brace_in_string_interps.html](unnecessary_brace_in_string_interps)

* Fix lint tests. analyze_once_test.dart and create_test.dart

* Make switch widget accept 3 other colors: inactiveThumbColor, inactiveTrackColor, activeTrackColor.

* Make switch widget accept 3 other colors.

* Make switch widget accept 3 other colors.

* _SaltedKey solution to `ExpansionPanelList`

_SaltedKey implementation courtesy of @Hixie
Tested and confirmed working.
Fixes #11166

* Added a simple test

* Style correction to test

(it's the command that populates the .packages file)

This makes command validation happen as part of `verifyThenRunCommand()`,
using a newly introduced protected method (`validateCommand()`) rather than
a `commandValidator` property (that subclasses were responsible for manually
invoking).

This picks up a skia roll, which fixes some black screens on Android emulator.

It was incorrectly added in #11858

Fix the documentation (it was just wrong before).

Add an explicit code path to handle horizontal overflow so that we
don't have a left bias.

Just some very minor tweaks to remove subtle LTR bias.

We use the same arrow rotation animation in RTL and LTR, but I think
that's correct. Usually, rotations are either clockwise or
anitclockwise, which are the same in RTL and LTR. We might need to check
with someone who reads an RTL language to confirm.

Fixes #11845

This widget makes it easier to animated Positioned widgets with
awareness of the ambient Directionality.

Fixes #11998

Previously, the rows and columns arguments had different semantics. Now
they have the same semantics. The new API also uses Iterable rather than
List to give clients more flexiblity in how they construct these
arguments. For example, RenderTable no longer needs to reify the
reversed list of column positions.

Also, fix asserts in TableBorder#paint to match documentation.

Fixes #12009