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.
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.
This patch prepares us to switch sending semantics information over mojom to
using dart:ui directly. Currently the recorded information is dropped on the
floor, but that will improve in future patches.
We now use JNI rather than Mojo to transport pointer data from Java to Dart.
Also, fill in a few more of the pointer data fields from information in Java.
* Namespaces have been updated to reflect the move from //flutter/sky/shell to //flutter/shell.
* shell/BUILD.gn file has been split into smaller GN files for each subcomponent of the shell (common, GPU, diagnostic, testing).
* GN dependencies have been rewritten to stop exposing common shell dependencies as public. Duplicates have also been removed.
* GPU subcomponent has been updated make it more suitable for Vulkan integration.
* The GLFW backend has been resurrected.
