Remove deapexer and prebuilt apex select mutators

Originally, when the prebuilt_apex was first created, it selected the
source to use in its DepsMutator. It did that because that was a
convenient place for it to perform that work which had to be:
* After the arch mutator had run so MultiTargets() was available.
* Before the prebuilt_select mutator runs as that relied on the Source
  property to have been set.

Change 064b70c9 then duplicated the call from the DepsMutator of the
deapexer module type that was added as part of the work to make dex
files available for hiddenapi processing.

Change 356f7d45 moved it out of the the DepsMutator methods into its
their own mutators, presumably because it interfered with the
Soong -> Bazel conversion work.

This change improves the existing PrebuiltSrcsSupplier mechanism to
support reporting errors so that the logic for selecting the source can
be done on demand rather than in separate mutators.

The main complication was that PrebuiltSrcsSupplier is called with a
BaseModuleContext for both source and prebuilt modules so it cannot use
any methods on it that are related to the current module. That
necessitated adding MultiTargets() to android.Module.

Bug: 181267622
Test: m droid
Change-Id: I106c78fd21016f051a315b82b470d8f12b1f820b