Minor improvements on ApiCallStats and ApiCallStatsTest.

ApiCallStats:
 - Make it final
 - Hide constructor
 - Encapsulated fields
 - Removed redundant @NonNull annotations
 - Throws (ISE instead of IAE) when both app and sdk name are set

ApiCallStatsTest:
 - Extends AdServiceUnitTestCase
 - Uses Truth instead of JUnit assertions
 - Added tests for equals() / hashcode() / toString()
 - Split testIncompleteInputBuilder_throwsIAE in 2 tests
 - Uses non-zero result code

Test: atest AdServicesServiceCoreUnitTests:ApiCallStatsTest
Bug: 270974848

Change-Id: I6d623cd549ccde12ba06d9bbfdd7b7fe4caf6666
3 files changed