[HostStubGen] preserve policy reason in generated jar

Now all the HostStubGen annotations has a "reason" field
which contains the "filter reason".

Also, store inline comments in the policy file in the "filter reason" too.

This means we can access information like "no-pta" in the policy file
at runtime, which would help analyze method call log.

Size impact:
Before:
    33986606 Jul  8 17:00 100-framework-minus-apex.ravenwood.jar
After:
    35639586 Jul 14 13:28 100-framework-minus-apex.ravenwood.jar

  -> ~5% increase
Before:
    231389156 Jul  8 14:56 SystemUiRavenTests.jar
After:
    234817831 Jul 14 14:43 SystemUiRavenTests.jar

  -> ~1% increase

Bug: 292141694
Flag: TEST_ONLY
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh -s
Change-Id: Ifa2c253f28714c193119357744d56cdfb4daee67