This reverts commit a48b5f6d.

Refactoring related to use of the embedder APIs on macOS
host builds.

* Revert "Pass option to reuse an existing runtime controller (#4253)"

This reverts commit 57f361dc.

* Revert "Document the Porter-Duff operators. (#4250)"

This reverts commit b15fa9c6.

* Revert "Move channel and codec related files to common (#4225)"

This reverts commit 674a3f58.

* Move channel and codec related files to common

This is in preparation for implementing channel and plugin support
for macOS desktop builds.

This is for Fuchsia where we would like it to be located at //third_party/flutter.

* Fix remaining ftl->fxl conversions

The previous scripting pass at this did not account for objective c file endings

* Update tonic DEPS reference to the post-fxl version

This repository contains FTL now in the Fuchsia build.

Update ICU to ToT and ensure that slimmed down versions of data files are shipped on the mobile platforms. (#4005)

This reduces the size of the ICU data files from 10.3 MB to 6.6 MB (uncompressed). Also allows us to remove version specific hacks from libTXT and dependencies.

Update targets only included in host_debug_unopt.

This reverts commit f5d0004e.

So `flutter run --local-engine=...` will work out of the box.

Fixes flutter/flutter#9154.

Breaking change: removed facilities for JSON and string messaging from FlutterView/FlutterViewController, leaving only binary messaging there. All other use of flutter communication now goes through FlutterMessageChannel and FlutterMethodChannels. Retained use of String and JSON codecs for now.

Companion flutter PR: flutter/flutter#8837

Flutter channels now also supported on iOS. Use FlutterMessageChannel or FlutterMethodChannel with binary/string/json/standard codecs.

* [iOS] Ensure FlutterMain is called before interacting with the engine in any way.

* Licenses

After this patch, we no longer link with Mojo. We still use some gn definitions
from //mojo to create Dart packages.

We no longer use mojom to transport messages. We still use the Mojo EDK
to spin the event loop, however.

Instead, just use JNI and Objective-C directly.

This patch removes the use of the host messages mojom and switch all
message routing over to platform messages.

Clients have been migrated to the TextInputPlugin.

This functionality has been replaced by the PlatformPlugin. Also move the
contents of //flutter/services/common to more sensible homes.

The platform use cases are handled by the PlatformPlugin. The media service and
the sensor service have no clients. If we want to use them, we should create
plugins for them.

Also, expose a convenience class for processing JSON messages.

We've cut over to the new semantics interface.

Instead, clients should use host messaging.