Add java.RegisterRequiredBuildComponentsForTest function

Insulate tests that exercise code in the java package from having to
register the build components provided by the java package by providing
a single function that registers them all. This follows the pattern
currently used in the cc and rust packages.

This change is in preparation for switching the dex_bootjars singleton
from a singleton, which does not require a module definition in order
to be instantiated, to a singleton module which does. That will require
adding a module definition into java.GatherRequiredDepsForTest() and
this change ensures that the required components will have been
registered in every test.

Bug: 177892522
Test: m nothing
Change-Id: I6475db8240894947dd07c89a940a3e4f201aa598