Move FlickerTests to frameworks/base/tests 2/2

platform_testing is moving to AOSP first development. FlickerTests may require access to
in development test apis and cannot be developed in AOSP.

Other minor changes:
- remove FlickerTests from APCT. FlickerTests will use TEST_MAPPING
- use @FlakyTest instead of @Ignore annotation to skip tests

Test: atest FlickerTests
Test: make -j32 continuous_instrumentation_tests
Test: cd frameworks/base/tests/FlickerTests/ && atest :postsubmit

Bug: 112044297
Change-Id: Icc3194ddd9b801034d8797bf2ec60ebff071612c