closes https://github.com/TryGhost/Ghost/issues/8729, closes https://github.com/TryGhost/Ghost/issues/8728
- remove the duplicated `max-height` rules for different parts of the power select dropdowns - they were interacting with each other and causing a large part of the lists to be unreachable
- bump the `bufferSize` so that enough dropdown items are rendered to fill the dropdown list
- filter the temporary tags that are created when using the PSM tags input so duplicates aren't visible in the tags dropdown filter
closes https://github.com/TryGhost/Ghost/issues/8540
- use `{{vertical-collection}}` in the tags dropdown filter list, opening the dropdown is now virtually instant as it's not attempting to immediately render components for every tag in the list
- remove pagination/infinite scroll from tags screen
- load all tags when accessing the tags screen
- will pause to show spinner if no tags have previously been loaded
- if tags exist in the ember data store, show the list immediately and load/update list in the background
- use `{{vertical-collection}}` to render enough tags to fill the scrollable area with a small buffer and use occlusion and element re-use to swap tags in whilst scrolling (suuuuper fast no matter number of tags loaded)
- scroll tags into view when they are selected (keyboard nav now makes a lot more sense)
- tested with 875 tags and 2x/5x CPU throttling with no major slowdowns 🎉
