Update public function documentation for Pbap Client

This change inherits the documentation from the parent class definitions
where it can, so our profile proxy can be more in line with others.

Ignore-AOSP-First: Mainline-related going into internal first
Tag: #refactor
Bug: 221880459
Test: atest BluetoothInstrumentationTests
Change-Id: I5189e7f172731b5b5c15a0df60a9197dc71301ae