Rate limit calls to AM.getMyMemoryState().

Apps do not need to call getMyMemoryState any more than 200 times per
second. Rate limit this API to 2 calls every 10ms which will allow
apps to keep getting updated info at a reasonable interval.

Flag: android.app.rate_limit_get_my_memory_state
Bug: 365182205
Test: atest ActivityManagerTest
Test: manually check logs for cache hits/misses
Change-Id: I0ab53c8f477dc5a82c812d1fe541491e04367cc9