2/Trimming tasks based on active and visibility

- Add logic to trim tasks beyond the max-recents policy, including
  migrating the trimming of quiet profile tasks and visibile tasks
  to the system (to ensure callers always get a consistent list)
- Remove trimmed recent tasks from the active task list
- Add logic to actually handle config_hasRecents to determine whether to
  apply visibility filtering (otherwise only filters by max-recents as
  before)

Bug: 34270611
Test: runtest --path frameworks/base/services/tests/servicestests/src/com/android/server/am/RecentTasksTest.java

Change-Id: If17586cd9e8ac1ae8f112239381adc96a0528123