Framework cleanup to prepare API change on permission

In order to smoothly merge aosp/3185962, this change is cleaning up some
annotation / code / various miscellaneous small fixes that helps
having a smaller "api change" CL.

Bug: 349682934
Test: m com.android.btservices
Flag: Exempt refactor
Change-Id: I624309d41db7c8af1a78409b3ebdf9e8cc68e284