Add `file_contexts` for Release Runtime APEX module.

Also rename `file_contexts` for the "Debug" Runtime APEX module
(containing both release and debug variants, as well as additional
tools).

Test: make com.android.runtime
Test: make com.android.runtime.release
Test: make com.android.runtime.debug
Test: art/build/apex/runtests.sh
Bug: 113373927
Change-Id: I6b917d7f5b1734aeb717932081c7b03366ef2774