Only update insetsHint while necessary

To improve the performance, this CL makes it only calculates and updates
insetsHint when:
- the insets source is visible at the server side.
- the insets source frame is changed.

Fix: 183739779
Test: atest --iterations 10 ImePerfTest#testHideIme
Change-Id: Ie4e6fe7af21a036dabbca71c9170f40e04997a13