bazel apex: Add mixed builds support for <module>_using.xml file.

This file contains the java APIs parsed by the 'dexdeps' tool within the gen_java_usedby_apex.sh.

Bug: 239084755
Fixes: 239084755
Test: presubmits
Change-Id: Ia271783a6be3ea3a343481306cde1aaba2166e88