* Retain the parent of a SemanticsObject

This fixes the last known crash in iOS accessibility.

* rework memory management

* review comments

***Turns on color correct rendering for Android and iOS
***Communicates dst color space to raster cache
***Turns on color space aware image decoding

Test:
***color_testing_demo on Pixel XL
***flutter_gallery on iPad Mini and iPad Pro (haven't figured out how to run manual_tests on iOS)

TODO:
I needed to split up this CL somewhere. These are follow-up tasks.
***Make desktop backends color correct
***Make debugging tools (ex: encoding frames to png) preserve color space
***Investigate using UIKit API to allow iOS to fine tune color space of rendered content

Disables auto-capitalization on iOS text fields for TextInputTypes other
than text.

Some keyboards (e.g., on some Samsung devices, SwiftKey) ignore
InputType.TYPE_TEXT_FLAG_NO_SUGGESTIONS and require
InputType.TYPE_TEXT_VARIATION_PASSWORD.

Adds support for requesting a platform keyboard optimised for entering
URLs.

Adds support for requesting a platform keyboard optimised for entering
email addresses.

* Enable software rendering backend on android. Add "enable-software-rendering" flag.

* Fix variable naming and threading.

Previously, taps were sent to the topmost tap handler in the center of the accessibility frame of the selected element nd therefore might have been handled by a different element than the desired one.

**This is a breaking change on iOS**

Previously, the `paused` state was entered when the application resigned
active status. `inactive` now maps to this status. `paused` now maps to
an app that has been backgrounded.

`inactive` is currently emitted on iOS only and corresponds to iOS's
foreground inactive state.

Current state transitions are:
`resumed` <--> `inactive` <--> `paused`

suspending is currently emitted on Android only and corresponds to the
transition to Android's stopped state.

Current state transitions are:
`resumed` <--> `paused` --> `suspending` --> `resumed`

These transitions may change in future.

I weaksauced

Android seems to do this by default. This way, if you select a table cell it will read the content of that cell.

* Fix crash in iOS accessbility

Previously, whenever an action would remove the focused element from the screen the app would crash. This change tells iOS to focus the first on-screen element after every change to the semantics tree. This avoids the crash.

In a future iteration, we should tell iOS which element it needs to focus by looking at the sematnics tree (instead of leaving it up to the iOS).

* Better handle the case were the focused element stays on the screen

* review comments

Use AudioServicesPlaySystemSound instead of AudioServicesPlayAlertSound.
This avoids the potential of a system beep on devices without support
for haptic feedback.

Scrollable elements can now be scrolled in accessibility mode and they scroll in the right direction.

Note: App crashes right after scroll finishes (that's a separate problem as the app currently crashes after every action performed in accessibility mode).

* AX fixes for iOS

With this, the accessibility frame (for VoiceOver, etc.) is drawn at the right position around a widget.

* review comments

Check incoming text editing state and only fire textWillChange:,
textDidChange:, selectionWillChange:, selectionDidChange: when the text
or selection actually changes.

On selectionWillChange: in a text field where auto-correct is enabled,
iOS will attempt to auto-correct the word preceding the cursor. This
change also updates the text before calling selectionWillChange: to
prevent auto-correction on the preceding value of the text field.

The core problem was multiplying matrices the wrong way around.

While I was there I did some minor cleanup. I think that may have
fixed another bug relating to A11Y turning on or off improperly, but
since I never figured out the steps to reproduce, it's hard to tell.

Fixes https://github.com/flutter/flutter/issues/7205
Fixes https://github.com/flutter/flutter/issues/10059 (maybe)

Having the device pixel ratio of the test shell be 1.0x makes it
unlikely that we will catch errors relating to mishandling of the
device pixel ratio in the test shell.

This patch arbitrarily increases the device pixel resolution while
keeping the logical resolution the same.

Handle willChangeFrame to handle keyboard show, resize, reposition
(split, move floating keyboard) events. Handle willBeHidden events for
keyboard dismissal.

Fixes incorrect bottom padding introduced in
f2581c9b due to didChangeFrame
notification firing after willBeHidden on keyboard dismissal.

This change brings iOS return key behaviour in line with current behaviour on
Android.

* Implements TextInputClient.performAction for iOS Adds FlutterTextInputAction
* enum Defaults return key to 'Done' Ends editing and hides the keyboard if
* 'Done' is pressed

Future work is planned to support configurable return/action key behaviour.
See: #9573, #9210, #8028.

Previously, the last error was a global static. Now it is a thread-specific
value, which means we need to visit the UI thread to read the value.

It controls whether the observatory and diagnostic server will
bind to the IPv6 loopback address rather than the IPv4.

Fixes https://github.com/flutter/flutter/issues/9813

Previously, it was a static. Doesn't have much effect in practice because we
only use this microtask queue for main isolates, which exist on a single
thread.