[Launcher] Add new logic for search providers to update results

The old callback used by the SearchProvider and SearchController
doesn't send enough information for the new ranking system, so this
implements a new SetResults method used only when categorical search
is enabled.

The SearchController now stores a map of provider types to results. The
'provider type' is currently just AppListSearchResultType, as that's
what SearchProvider::ResultType returns. We might need to update this
to another enum in future, but for now it's okay.

Bug: 1199206
Change-Id: I248a09eb0b9c9d37151e8c7f1bb2f3e3eceeac61
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2855145
Reviewed-by: Rachel Wong <wrong@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#877339}