Rename permission group to "Nearby devices"

This renames the "Nearby Bluetooth Devices" group to "Nearby devices",
and changes the associated icon to a more generic,
not-specifically-Bluetooth icon.

The reason for this is that we will soon be adding non-Bluetooth
permissions to this group (i.e., UWB).

Bug: 183988398
Test: manual
Change-Id: I555860880c981171f0bff7f11695a03a0f8de586