Historically, the code related to the rollup search in TSVB was added to the x-pack/rollup plugin. And now the rollup plugin has a folder specific only to TSVB (see x-pack/plugins/rollup/server/lib/search_strategies)
IMO, this is a design issue because usually a TSVB plugin should depend on a Rollup plugin, but not vice versa.

On the other hand, in #76274, we started using a new Search API that natively supports search by rollup data.

I think we should:

1. check which logic we still need from x-pack/plugins/rollup/server/lib/search_strategies and which can be reused from the data plugin
2. create a new vis_type_timeseries_enhanced plugin and move into it related code
3. use new Search API for searching by Rollup data