Delegate work of apexInfoMutator to ApexInfoMutator interface

Refactor the apexInfoMutator to delegate the work to an implementation
of ApexInfoMutator and then move the existing functionality into the
apexBundle.ApexInfoMutator(). This will allow a follow up change to
customize the behavior of this mutator for prebuilt_apex modules.

Test: m nothing
Bug: 171061220
Change-Id: I7ccd55818e02a606c5494e215f4370b635ddd0a5