SkyApplication now reads service info from a services.json file bundled
with the apk. For each service, it registers a method that invokes
connectToService on a named class. This way, third party services can
register themselves.
There's a corresponding change to flutter_tools to generate this
services.json when building an apk that depends on services.
* Include all the artifacts required to build an APK package
* In addition to the zip, some files will be uploaded separately:
* libflutter_library.so (large debug symbol library)
* flutter.mojo (needs to be downloadable from the target device)
