Adding public event callback instead of the internal one to UiAutomation.

It appears that com.android.internal.util.Predicate is in the public
APIs but it is in the internal package. Leaking the predicate APIs is
a mistake and while we cannot fix that, this change is adding legit
public filter interface.

bug:8183223

Change-Id: I3e2c0ef685d7a832630aaa3ec2e8eae3fb058289