Refactor cache behavior from "atmoic" to "group".

Using the word "atomic" has too much baggage relating to locking
guarantees, so move to something softer.

Add isQuotaSupported() for CTS tests.

Move CacheQuotaStrategy over to using SparseLongArray, which has a
more efficient memory footprint inside the system server.

Test: cts-tradefed run commandAndExit cts-dev -m CtsAppSecurityHostTestCases -t android.appsecurity.cts.StorageHostTest
Bug: 35812899, 35684969, 36482620
Change-Id: I894f53e6f3bc76c77d1bb18c51db14833df14a49