Combine hidden API encoding with flag generation

Previously, the rules to perform hidden API encoding were generated
separately to the rules to perform hidden API flag generation. This
change combines them within the (renamed) produceHiddenAPIOutput()
method and makes the paths to the encoded dex files an output of the
generateHiddenAPIBuildActions method alongside the paths to the
generated flag files.

As encoded dex jars are now an output of the produceHiddenAPIOutput()
method which is implemented for both prebuilts and source
bootclasspath_fragment modules that necessitated the prebuilt also
providing paths to encoded dex files. That in turn required updates to
some of the tests to provide dex files from prebuilt_apex modules.

Similarly, as the produceHiddenAPIOutput() method may not be called
for some bootclasspath_fragment modules as they do not yet provide all
the information needed to perform hidden API encoding then it is
necessary to extract the encoded dex files produced by the modules
themselves. That also required a few changes to tests that did not
previously provide dex files.

Bug: 177892522
Test: m com.android.art
      - check that this change does not change the contents of the apex
        file, i.e. is byte-for-byte identical.
Change-Id: I60996a34d06ed1c87ed244ab3509621999ad86ec