Add SettingsPrefController for Slices

Adds a new abstraction layer between preference controllers
and the AbstractPreferenceController. The layer is used to
consolidate the logic for each the setting type for getting
and setting values. This will be extended to support UI
information for Slices.

For reference how this fits into Slices, look at the
like-named classes added in this prototype:
ag/3221891

The changes in Search are as a transition into deprecation.
The code for Search in Settings is out-of-date from the
unbundled counterpart, and this change is made so that the
current code behaves as normal.

Test: robotests
Bug: 67996707
Change-Id: Ib1faab706485039edad66119a27a3fd5cabe6009