Bluetooth: Dismiss pairing dialog on user click

* Existing pairing dialog should be dismissed when user clicks on Yes/No
* In a pairing session with multiple pairing dialogs, this is necessary
  as otherwise the second pairing dialog will not be shown
* Modified unit test to test this behavior
* Launch pairing dialog as UserHandle.CURRENT to avoid Context warnings

Bug: 35833536
Test: make, unit test, pair with Bluetooth devices
Change-Id: I1823b78d287134505f59eab7caca2329ecc3a36f