* Add default color for cursor match
Not all terminals support dim, for those terminal that does not support
this (konsole, item2, wezterm), users cannot differentiate between match
and primary cursor. So set a color for this.
* Use alacritty dim color for match
Adds `ui.linenr.selected` which controls highlight of linu numbes which
have cursors on.
- Fallback to linenr if linenr.selected is missing
- Update docs and themes
- Add TODOs for themes with temporary linenr.selected