Add more tests for the devicepolicy processor

Check for more expected errors and make sure that the invalid java files
compile fine without the processor.

Bug: 433951378
Flag: TEST_ONLY
Test: atest frameworks/base/tools/processors/devicepolicy/test/src/android/processor/devicepolicy/test/PolicyProcessorTest.kt
Change-Id: I27ce3e9d7f58b935a857df18a053678a1dfd26fc