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