Create AndroidLibraryPlugin to share common module configuration.

First step in cleaning up duplicate code in build.gradle config files.

This CL relands ag/1746409 that had to be reverted due to not listing all the maven
repositories in buildSrc/build.gradle.

Bug: 33845666
Test: ./gradlew clean assemble assembleAndroidTest continues to work
Change-Id: I335c4366a015efa7eab880cd8d01659c41f1abb2
30 files changed