Draft: Overhaul search UI
This merge request lays a lot of the groundwork towards implementing the improved Dolphin search UI/UX as discussed in #46.
Big differences to the UI/UX discussed in #46:
- A toggle to change the search tool is provided as most contributors deemed that useful in !642 (comment 985112).
- The "chips" are missing which show filters while the popup is closed. (<-This should probably be implemented before merging this incomplete UI overhaul makes sense.)
- The search results are still not split between file name matches and file content matches or similar.
- The filter bar has not yet been combined with the search in any way.
I don't really have plans to continue with this work, because I am busy with other stuff. Everyone is welcome to push changes to this merge request. Just make sure that you don't silently drop other people's commits. Reverts are fine.
The code that is already there is neither final nor polished.