Restore session on new window after app kill

Also:
- Give the session an integer ID as the activityToken is not stable over
  restarts of the activity
- Verify that session is only accessed by one UID
- stabilize AccessibilityViewIds over activity lifecycle at least for
  the IDs we can do that. This required to split the ID namespace in
  "per-app" and "per-activity" views. Only the later ones can be
  restored.
- Do not end session when app is killed (as it can be restarted)

Bug: 35484143
Fixes: 36392498
Test: cts-tradefed run cts-dev -m CtsAutoFillServiceTestCases --test=android.autofillservice.cts.SessionLifecycleTest
      cts-tradefed run cts-dev -m CtsAutoFillServiceTestCases
Change-Id: I229acc1b3ce35fb57262da7d7466b5d4328b49d4