Highlight instead of filter embedding view

The embedding view currently only supports filtering, not highlighting. We could instead sho the unfiltered data as the background distirbution.

Start by locating the embedding view and reading the existing filtering flow. Determine how the unfiltered data can remain visible as the background distribution while the selected subset is highlighted; done means the view supports highlighting without losing the current filtering behavior.

Written by the indexing model from the issue text.