android.test.mock is built with much less number of sources

android.test.mock is built with its own sources plus a small number of
framework sources that provides private APIs that the library's APIs
have references to. Previously, it was built with the entire framework
sources which is too many and should have slowed the build performance.

Bug: 141149570
Test: m
Change-Id: I165ffdfc053a71b323ef7058651d5908df06870f