Separate vdex versioning into two sections: verifier deps and dex code.

The layout is still the same, but this CL allows updating the cdex and
quickening encoding versions without having to update the verifier deps
version.

bug: 63920015
Test: test.py, dex2oat_test, oat_writer_test, oatdump_test
Change-Id: Ifd282b4c1856f7597d8d26577bf58b9ad87da084