This re-implements keyboard text selection so that it will work on platforms other than Android (e.g. macOS, Linux, etc.).

Also, fixed a number of bugs in editing selection via a hardware keyboard (unable to select backwards, incorrect conversion to ASCII when cutting to clipboard, lack of support for CTRL-SHIFT-ARROW word selection, etc.).

Did not address the keyboard locale issues that remain, or add platform specific switches for the bindings. All that will need some more design work before implementing them.

Related Issues
Fixes #31951

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

There were four or five different implementations in various tests for sendFakeKeyEvent, which roughly all did the same thing. I was going to add yet another one, and decided that it needed to be generalized and centralized. This replaces those instances with something that just takes a LogicalKeyboardKey so that it's self-documenting, and can be used with multiple platforms.

This adds two functions to widget tester: sendKeyDownEvent and sendKeyUpEvent which simulate key up/down from a physical keyboard. It also adds global functions simulateKeyDownEvent and simulateKeyUpEvent that can be called without a widget tester. All are async functions protected by the async guard.

* Fixed Selectable text align is broken

* Moved the default BinaryMessenger instance to ServicesBinding

This reverts commit 821602ae.

* Added assertion in defaultBinaryMessenger. Also fixed the devicelab tests.

This reverts commit 92ef2b9c.

This requires either runApp() or
WidgetsFlutterBinding.ensureInitialized() to have been called before
using any MethodChannels. Plugins broadly rely on MethodChannels and
right now there's no general requirements that they be constructed
within the runApp call, so the ecosystem breakages from this are broader
than originally thought. Reverting for now.

Guard removePointer with addTearDown to avoid cascading test crash.

reland Enable selection by default for password text field and expose api to turn on and off context menu options (#37324)

Revert "reland Enable selection by default for password text field and expose api to turn on and off context menu options (#34676) (#37183)" (#37295)

This reverts commit 7eb09a84.

reland Enable selection by default for password text field and expose api to turn on and off context menu options (#34676) (#37183)

This reverts commit 48c7090f.

Revert "Enable selection by default for password text field and expose api to turn on and off context menu options (#34676)" (#37055)

This reverts commit 0d0af315.

Enable selection by default for password text field and expose api to turn on and off context menu options (#34676)