japicmp should fail when new methods are added to public interface

At least twice in 1.15.0 (commits 7aa03824 and b377e3f8), new methods were added to Geode's public API (such as `GatewaySender.getRetriesToGetTransactionEventsFromQueue`).  While adding methods is compatible with existing source and binary calls to this interface, it breaks anything else that implements this interface. Even if a default implementation had been provided, there are still edge cases where it could collide with existing implementation that may already have methods with those names.  These two examples have been fixed now by GEODE-9629 and GEODE-9630; this ticket is to fix CI to prevent this in the future.

Our required PR check "api-check-test-openjdk11" should have prevented this from happening...