[Pandora] Move pairing interface into a separate interface

As per offline discussion, all pairing/bonding related interfaces for
both classic + LE will be moved out of Host (since Host is getting huge)
and put in a separate interface. We can't call it SM since we have
classic stuff in here too.

Test: existing PTS
Bug: 242326310
Tag: #refactor
Change-Id: I2704098edd72e50d53366b210a2bf425f11d3388