NoMan bubbles policy: remove non-communication bubbles when app is foreground

We're no longer allowing any notification to be a bubble if the app is
foreground when the notif was sent; it must always fulfill the communication
policy.

- removed check & FLAG_BUBBLE when app is foreground
- removed the tests for FLAG_BUBBLE on foreground produced bubbles
- added a test to ensure that FLAG_BUBBLE doesn't happen just because the
  app is foreground
- attempted to clean up some of the bubble helper methods

- no foreground service bubbles unless its a phone call (test for this
  in CTS CL)

Test: atest NotificationManagerServiceTest
Test: atest NotificationManagerTest (needs CTS CL)
Bug: 138116133
Bug: 144352570
Change-Id: Idba370c23a3ccaa6479f61a94632f29d623a1e76