Add / fix a few tests

- Make ActivityThread a bivalent test.
- I turned ActivityThread.getSystemContext() returns a context with
  an "android" package. Updated the test and excluded it on ravenwood.

- Added tests for accessing static mocking from other threads.

Bug: 292141694
Test: atest RavenwoodMockitoTest_device RavenwoodBivalentTest_device
Test: atest RavenwoodMockitoTest RavenwoodBivalentTest
Flag: TEST_ONLY
Change-Id: Ifdb25e6d42e6ac710c4879245b4159a572a483eb