Prepare for compat-framework support

- Create a Context for the system server
- Add the target SDK level to RavenwoodConfig
- Allow PropertyInvalidatedCache sysprops
- Copy StatsD classes, until we get a proper support
- Copy Compatibility and some annotations from libcore
- Keep FrameworkStatsLog

Flag: EXEMPT host test change only
Bug: 292141694
Test: $ANDROID_BUILD_TOP/frameworks/base/ravenwood/scripts/run-ravenwood-tests.sh
Change-Id: Ib572d1b25c47c693b4969d12490e593dc5f48eb1