Rename FingerprintGestureCallback.onGesture

Renaming to onGestureDetected.

Deprecating onGesture. It needs to be removed for release.
Leaving it in to avoid breaking TalkBack, which is using it.

Bug: 37708057
Test: Accessibility unit and CTS tests still pass.
Change-Id: Icd66889216fc978ad6d27aa83a8c8d13869daad3