[HostStubGen] Multiple improvements

1. Consolidate SubstituteAnd[Stub/Keep] into a single Substitute policy.
   There is little reason to support SubstituteKeep, so make Substitute
   implicitly Stub. In production, methods are never annotated with both
   Stub/Keep + Substitute anyways.
2. Update ClassFilter to support nested classes.
3. Rewrite AnnotationFilter with the following improvements:
   - Previously, when a method is annotated as Substitute, the method
     itself will get the Remove policy, and the replacement method will
     get the Stub/Keep policy. In the new implementation, the annotated
     method will preserve its Substitute policy, which will not only be
     useful for future improvements, but also be consistent with how
     text policy filter is implemented.
   - Process the entire class all at once and cache its results; the
     previous implementation re-run the same operations multiple times.
   - Previously, the annotation allowlist was not properly enforced when
     Substitute annotation is used.

Bug: 292141694
Flag: EXEMPT host test change only
Test: atest hoststubgen-test-tiny-test
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh
Change-Id: Iee223c5d0814351eccdcfc884da64bc507af83b7