releasetools: Add support for compressed APKs.

Compressed APKs can be identified by a "compressed=<ext>" entry in
the apkcerts.txt file. When we encounter such an entry, we need to
decompress the file to a temporary location before we process its
certs. When we're signing, we should also recompress the package
after it's signed.

Bug: 64531948
Test: ./build/tools/releasetools/check_target_files_signatures.py
Test: ./build/tools/releasetools/sign_target_files_apks.py
Test: compared signed output before / after this change, verify that
      it's bitwise identical when no compressed APKs are present.

Change-Id: Id32e52f9c11023955330c113117daaf6b73bd8c2