This further addresses https://github.com/flutter/flutter/issues/14568.

So tool_tests-windows won't fail.

* SystemNavigator.pop can pop w/o UINavigationController

* Fix a compilation problem when  using iPhoneOS12.0sdk(Xcode10).

Also teaches FML to create files and directories.

This will not be active on the Framework until https://github.com/flutter/flutter/pull/22221 lands.

Format code from previous patch

* If isolate is already running, return true

* Use shell::Engine::RunStatus as result of Engine::Run

Use a screen height ratio to determine if the keyboard is onscreen or not. This is used because Android does not provide a deterministic API to detect this.

We remove the padding when the keyboard is closed and the inset is due to the hidden navigation bar, otherwise, we apply the full keyboard inset.

* Change FlutterDartProject to keep precedence when looking for the assets bundle

* Change assetsPath to fallback to mainBundle when the defined bundle does not contain assets

This shell used to serve the dual purpose of running Flutter tests as
well as optionally being able to run Flutter applications on a Mac
desktop. After all the test runner targets were consolidated
(flutter_tester), this target was no longer used to run the tests. This
target is currently only used by engine developers to test changes
quickly on the host. Even for this purpose, the Desktop embedders are
more full featured and use the stable embedder API. The presence of a
cross-platform tester target, alternatives for Desktop targets that use
the stable embedder API and the fact that this target is no longer
tested, makes having this code in the source entirely redundant.

* Make FlutterStandardCodec handle writing NSData

iOS developers can accidentally pass an `NSData` object directly to
`FlutterStandardCodec` and forget to wrap it in
`FlutterStandardTypedData`.  This failure won't be caught until
runtime.

Let's make `FlutterStandardCodec` more tolerant by making it assume
that `NSData` should be treated as a binary blob and by wrapping it
automatically.

Fixes https://github.com/flutter/flutter/issues/17449

Testing Done:
* Made a sample Flutter iOS application that created a
  `FlutterMethodChannel` and invoked a method using an `NSData*`
  argument.  Verified that the Flutter method handler received the
  message and that the `MethodCall.arguments` was a `UInt8Array` that
  preserved the original byte order.
* Verified that without this change, the same sample application
  crashed when run in debug mode.

* Add a unit test for encoding raw NSData

* Formatting adjustments

Decouple PlatformViewsController from FlutterView.

Instead of getting a FlutterView instance, depend on the specific interfaces required by
PlatformViewsController (BinaryMessenger, TextureRegistry, and Context).

This allows using PlatformViewsControlling in the flutter/embedding
code.

Revert "Fix a compilation problem when using iPhoneOS12.0sdk(Xcode10) && clang version 7.0.0." (#6307)

* Revert "Add logging if FlutterDartProject fails to load the application kernel snapshot (#6257)"

This reverts commit d29c7db7.

* Revert "Update deprecated subtags from language subtag registry. (#6280)"

This reverts commit 2a1debfc.

* Revert "Add Xib splashscreen support (#6289)"

This reverts commit 540cd962.

* Revert "Fix a compilation problem when using iPhoneOS12.0sdk(Xcode10) && clang version 7.0.0. (#6279)"

This reverts commit 05f21e63.

To make "Engine run configuration was invalid." failures (e.g.
https://github.com/flutter/flutter/issues/20777) a bit easier to
diagnose, add some more logging to `FlutterDartProject` to verify
that snapshot assets were properly bundled.

On the iPhone X, raising the keyboard sets a bottom physical inset equal
to the keyboard height, however we previously did not zero out the bottom
physical padding. This was incorrect; when a soft keyboard is present,
it 'consumes' the safe area inset for the home indicator widget,
eliminating the need for the app to handle this at all.

* Fix Top, Left, and Right padding for fullscreen apps.

* Fix minor nits and comments, simple logic inversion

Following fixes in dart-lang/sdk@91cbb57cd5cd012d5aa66bfb6eb3a1306271f431

Some developers might prefer launch images.

This reverts commit e3133e0e.

 - Add missing Dart 2 flags to gen_snapshot invocation.
 - Disable brittle service test.

This updates the embedder API but introduces no breaking ABI/API
changes.

This reverts commit 4c2448d1.

 - Switch core snapshot to Dart 2 and remove support for loading platform.dill.
 - Remove support for loading script snapshots.
 - Remove support for loading source.
 - Remove settings and fix names to reflect the above.
 - Remove support for loading the service isolate from source.

See https://github.com/flutter/flutter/issues/21348

* Roll buildroot to be483cb1cd3a9c4313b2e534034d23a05c3d849e
* Rolls buildtools to c1408453246f0475547b6fe634c2f3dad71c6457

This fixes flutter/flutter#20788

To fix the Fuchsia build.

Fixes #9627

The tools are now placing icudtl.dat in the flutter_shared directory.
It is no longer necessary to check for this asset at its previous path.