Restrict PIC test APIs to testing

Test APIs are now guarded so that they throw if the current process is
not a test.  This behavior is gated by an existing PIC test flag.

Flag: android.app.enforce_pic_testmode_protocol
Bug: 396173886
Test: atest
 * FrameworksCoreTests:PropertyInvalidatedCacheTests
 * FrameworksCoreTests:IpcDataCacheTest
 * CtsOsTestCases:IpcDataCacheTest
Change-Id: I0cb08e03b4b44808dc95294c73b0b838e5ea56e3