Preserve certain "Nearby devices" implicit grants.

We're willing to preserve an implicit "Nearby devices" permission
grant if this app was already able to interact with nearby devices
via background location access.

If the app doesn't have background location access, then the implicit
"Nearby devices" grant will be revoked as normal.  If the "Nearby
devices" permission had already been revoked through some other
means, it will remain revoked.

Bug: 195931693
Test: atest CtsPermission2TestCases CtsPermission3TestCases
Change-Id: I7d8df91954525da6473f70cb1759d9507e6a5606