aconfig: generate full fakefeatureflagsimpl in prod mode

This change will generate full fakefeatureflagsimpl in prod mode.
FakeFeatureFlagsImp will be the same in test mode and the prod mode.
FeatureFlagsImpl will be all unimplemented in test mode. setFlag,
resetAll are added into the interface FeatureFlags.

The reason to make this change is for project using injection pattern,
the project doesn't have to use test mode to test the flag guarded code.
The project can directly use the FakeFeatureFlagsImpl for testing.

Bug: 294838180
Test: atest AconfigJavaHostTest --host AND atest aconfig.test.java
Change-Id: Ib6d40fd3a9ef872e01594fd4f8d6c4cb10bb173a