As proof of concept for the dependency process from issue 794210, we want to start updating and loading the support library via android_deps. As the support library is used in a lot of libraries, it will also be needed for Dagger, so that's also an initial step for issue 787005


# Support Lib declaration cleanup

A side effect of the android_deps migration is that the visibility of transitive dependencies will become restricted. We currently declare com.android.support:appcompat-v4 and com.android.support:appcompat-v7 as dependencies, but not some lower level dependencies that get transitively downloaded like fragment-compat. As a result they will become hidden and unusable in other targets. We currently already pull these libraries trough umbrella targets for v4 and v7, but still explicitly list the transitive dependencies. These will need to be cleaned up as they are redundant now and will break in the future.

# Migration details

The dependencies will be available for some time from both android_deps and the current android_tools/sdk.. location, with a GN flag used to switch between them, and will eventually get cleaned up once regression and breakage risks are cleared.