Add dependencies from platform_bootclasspath to contents

Adds a FinalDeps mutator to add dependencies from the
platform_bootclasspath to the configured boot jars which can be from
either the platform or any apex. It adds dependencies for every
configured boot jar, whether in ArtApexJars, BootJars or
UpdatableBootJars.

At the moment the dependencies are only used for testing purposes
but following changes will make more use of them.

Bug: 177892522
Test: m nothing
Change-Id: I981305bf45bc20539a3d36987252f490e2b885cc