Fix the way manifest fixer detects optional <uses-library> entries.

Previously manifest_fixer used a naive way to distiniguish optional libs
from required ones: it checked if a library is on the list of optional
compatibility libraries. This works for compatibility libs, but not for
other libs.

Now we properly track optionality through all stages of the build,
starting with the addition of the library as a dependency (here's where
the `uses_libs`/`optional_uses_libs` distinction kicks in), store it in
dependency tag and propagate to class loader context, and from there to
the manifest_fixer.

The tests have been updated accordingly.

Bug: 196377222
Test: lunch bertha_x86_64-userdebug && m droid dist cts mts
Change-Id: I3631ce59ebe47116ce7a9b3d33a86f636846ef0f