Extract remote insets controller out of DisplayImeController

- Moved into DisplayInsetsController so that other shell components
  can listen to changes as well
- Expose the insets to DisplayController's DisplayLayout so that we
  can account for the extra nav bar insets from the task bar

Bug: 182905588
Test: atest DisplayInsetsControllerTest
Change-Id: Ie481282c9a71e02a77ce6b2cf8c2dcf4b8e452c6