Account for per-edge cutout for system gestures

- Currently, the start threshold for all edges is determined by the
  status bar size in the current orientation.  On devices with notches,
  the device overlays override the status bar height to include the
  cutout size, which results in a large threshold on all sides which
  causes touch issues with games (especially now that the game
  dashboard overlay shows with the bars).

  Instead, we can use a standard threshold size for all edges and only
  expand to account for cutouts on each edge respectively.

Bug: 195794974
Test: Without cutout, portrait/landscape app use default threshold
      With cutout, only the edge with the cutout has a non-default
          threshold
Change-Id: Iff7fc98b4fcbb9b78fd5b22bcc07357d7171a9f9