Define a @SystemApi string ID for each App Op.

Internal numeric op codes may change, but the public string IDs must consistently refer to the same operation.

Bug: 63907873
Test: Ran the tests being added in this this topic: make CtsPermissionTestCases -j32 && cts-tradefed run singleCommand cts-dev -m CtsPermissionTestCases --test android.permission.cts.AppOpsTest
Change-Id: I12bd9e2384d938120a403c4d76be4c1479ffd4ee