Add dependencies for files in LOCAL_PROGUARD_FLAGS

Do this by introducing a new LOCAL_PROGUARD_FLAGS_DEPS variable that we
can modify anytime we add a file reference to LOCAL_PROGUARD_FLAGS.

An alternative would have been to switch to LOCAL_PROGUARD_FLAG_FILES,
but that would have been much harder to ensure the same command line
ordering.

Bug: 130111713
Test: treehugger
Change-Id: If367197b30d563e0796f0cafa00be1f275f2c406