Refactor Mockito init to follow best practices.

Replace deprecated MockitoAnnotations.initMocks(this) with the
recommended @Rule public final MockitoRule mocks = MockitoJUnit.rule();
to adhere to Mockito best practices and ensure cleaner, more
maintainable test code.

Bug: 354063239
Test: atest FrameworksCoreTests WmTests
Flag: TEST_ONLY
Change-Id: I411a3cc25c16076b71d8ea83f0e6bb6656611552