Replaces the autocomplete overlay for categories and usernames on the search input and adds suggestions as items in the search results instead. Also adds the same behaviour for @mentions as well as special `in: status: order:` keywords. See PR for more details.
A followup to e3b0abc and a replacement PR for #13298.
Fixes long topic titles wrapping to a separate line in the dropdown search results.
Also replaces divs that were incorrectly nested inside spans.
When the admin creates a new custom field they can specify if that field should be searchable or not.
That setting is taken into consideration for quick search results.
A first step to adding automatic dark mode color scheme switching. Adds a new SCSS file at `color_definitions.scss` that serves to output all SCSS color variables as CSS custom properties. And replaces all SCSS color variables with the new CSS custom properties throughout the stylesheets.
This is an alpha feature at this point, can only be enabled via console using the `default_dark_mode_color_scheme_id` site setting.
