MediaSession2: Fix bug in MediaSession2.setCustomLayout()

There had been a bug that only the MediaBrowser2 can receive the change
in the custom layout.

This CL fixes the issue by moving code related with getting custom
layout change from MediaBrowser2Impl to the MediaController2Impl.
Related tests are also added.

Test: Run all MediaComponent tests once
Change-Id: If5ce1be19057af306f46f1b1ab64f18e3f3fb7bd