Make sure PIN edit control is focused

When doing Bluetooth pairing and the dialog reqesting a PIN comes up, we
want the PIN field to be focused and the keyboard to be shown. This fixes
a regression from N.

Bug: 62857671
Test: make RunSettingsRoboTests
Change-Id: I00dabfda737b6ac61b50518e11f21e5f9a5a1be1
(cherry picked from commit 4d7df06e)