Storage Refactor: Introduce PbapClientContactsStorage

This change combines the concepts of our Account Manager and Storage
interfaces (not currently centralized) into a single storage abstraction
called PbapClientContactsStorage.

This object owns storage accounts (a wrapper on Account Manager
accounts), storage interfaces, intialization (clearing of stale accounts
and data, etc.), and clean up (final bulk deletion of data on stop).

It's to be owned by PbapClientService, who will start and stop it (i.e.
own the lifecycle). State Machines will use a reference to this object
to create accounts, get notified when their account is ready, store
download results, and clean up contacts and call history upon
disconnect. This will come in a future change with a new State Machine

Bug: 376461939
Bug: 365626536
Test: atest com.android.bluetooth.pbapclient
Change-Id: Ibd14f91ca5f5e85b9ab78dbb61b2ab175f73a692