dexdump: fix xml output for jars containing multiple .dex files

When an input file (.jar/.zip) contains multiple dex files their
xml output goes into one api element. Previously, dexdump emitted an
api element per input.

Add a test that generates a multi-dex jar and checks the output.

Bug: 172042691
Test: art/test/dexdump/run-all-tests
Change-Id: I28b60d5a4b536d5ed6feb05c2476d58c00a33b68
6 files changed