AppErrors: Refine notion of "interesting" processes for b/g ANRs.

- SystemUI is always interesting, regardless of whether it's currently
  displaying any interesting activities or not.
- Any process that hasOverlayUI or hasTopUI is considered interesting.
- Any process that hosts an active foreground service is considered
  interesting.

Bug: 36383925
Test: manual
Change-Id: I852a00344f913200020c4f80500e38ff101fe05d