Update FocusFinder

Don't return the current view when finding the next or previous view.

Bug: 158492287
Test: atest cts/tests/tests/view/src/android/view/cts/FocusFinderTest.java
atest frameworks/base/core/tests/coretests/src/android/view/FocusFinderTest.java

Change-Id: Ib5c1854d1a13b9469ca55dfbf0be61bead47e29e