Ignore regions specified by the nav bar overlay

- We normally allow back regardless of system exclusion regions set
  to prevent games from disabling it entirely, so we need to add
  a side channel for the shortcut bar to exclude the region for
  pulling itself in.

Bug: 188095560
Test: Enable shortcut bar, drag from edge
Change-Id: Id5bf22ad2f8efb6ffb388e9aa5664936e2ad6a9d