Ravenwood support for feature flags.

Since feature flags are becoming an important part of development
work, ensure that Ravenwood tests can use existing tools such as
`SetFlagsRule` to populate values for code-under-test to consume.

To enable this, we extend `AndroidHeuristicsFilter` to recognize
feature flags generated code, and include that in the Ravenwood
environment by default.

Bug: 311370221
Test: atest FrameworksCoreTestsRavenwood FrameworksCoreTests
Change-Id: I526af65f816d153cb6e365cf6810a5a304d3e6a6