Move search querying into a single API

Settings now collects search results from a single
loader which fetches from an aggregator. This is to
facilitate the separation of search functionalitiy,
where "query" becomes a single synchronous call.
In this case, the aggregator will move to the
unbundled app and would be called on the
other end of the Query call. i.e. the new search
result loader will just call query, and unbundled
search will handle everything else.

An important implication is that the results will
be returned in a ranked order. Thus the ranking and
merging logic has been moved out of the RecyclerView
adapter (which is a good clean-up, anyway).

The SearchResultAggregator starts a Future for each
of the data sources:
- Static Results
- Installed Apps
- Input Devices
- Accessibility Services

We allow up to 500ms to collect the static results,
and then an additional 150ms for each subsequent
loader. In my quick tests, the static results take
about 20-30ms to load. The longest loader is installed
apps which takes roughly 50-60ms seconds (note that
this will be improved with dynamic result caching).

To handle the ranking in DatabaseResultLoader,
we start a Future to collect the dynamic ranking before
we start the SQL queries. When the SQL is done, we
wait the same timeout as before. Then we merge the
results, as before.

For now we have not changed how the Dynamic results
are collected, but eventually they will be a cache
of dynamic results.

Bug: 33577327
Bug: 67360547
Test: robotests
Change-Id: I91fb03f9fd059672a970f48bea21c8d655007fa3