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

Now they all flow through some common routines.

Now we just pass the data directly.

Causes warnings in Xcode.

Previously, these signals were sent over Mojo. Now we send them through
platform messages.

Instead, just use JNI and Objective-C directly.

We no longer offer mojo handles via this mechanism.

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 plugin is implemented internally by the engine to integrate with the asset
system.

Previously we had a mix of the two.

This patch is an attempt to fix a mysterious failure on the buildbot.

This plugin will eventually replace keyboard.mojom.

All the clients have migrated to platform messages.

This will replace raw_keyboard.mojom.

This patch completes the routing for Java-to-Dart platform messages.

This will eventually replace the clipboard mojom.

The function we were using to initialize this NSString assumed that our
UTF-8 data was null-terminated, which wasn't a valid assumption.

Fixes https://github.com/flutter/flutter/issues/6359

This functionality has been replaced by the PlatformPlugin.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

Add plunbing for Host-to-Dart platform messages

We'll use the plumbing in this direction for things like key events.

To make the default state all zeros.

Fixes https://github.com/flutter/flutter/issues/6236

Previously we were rounding event time stamps to the nearest second
because ftl::TimeDelta::FromSeconds takes an integer number of seconds.
Now we just convert directly from floating point seconds to
microseconds to avoid losing precision.

Fixes https://github.com/flutter/flutter/issues/6313

This method will let us remove the activity service.

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.

Fixes https://github.com/flutter/flutter/issues/6303

Also, expose a convenience class for processing JSON messages.

After this patch, the PlatformPlugin has all the required functionality on Android.

The PlatformPlugin is the first of the built-in plugins that will replace the
mojom platform services.

After this patch, platform messages now take the same path through the system
that semantics data does (on Android). Support on iOS will be in another patch.