Index Data to build Slices in Settings

The indexing is done by taking the indexable fragments from
search, grabbing their XML via SearchIndexableResources, and
then looking for controllers defined in preferences.

For each controller found, we take the combination of the
fragment providing the XML and the Preference info to create
an indexable row.

Buiding a Slice will be handled in a subsquent CL, but a
prototype can be found here: ag/3324435

Test: robotests
Bug: 67996923
Change-Id: I48668618079bcc3da55ab77b7323ee8e467073af