[Tagging] Update the "taxonomy detail view" to match UX design for displaying/expanding tags #155

This is a placeholder task for updating the "Taxonomy Detail View" to allow expanding/collapsing sections as shown in the Figma design.

Details TBD after testing of the initial bare bones version (#138) and changes from #110

For this task:

• For small taxonomies load them all at once but display them collapsed (REST API already supports this)
• When expanding a tag to show its children, load them if needed. Paginate them with "Load More" button if needed.
• When child tags are expanded, show child tags on the same background color as their root tag - see [Tagging] "Bare Bones" Taxonomy Detail Page #138 (comment)
• Ensure the implementation will be compatible with:
  • [Tagging] Keyword filtering of a Taxonomy's tags #128
  • Moving tags around in the editor by drag and drop (no story for this yet)
  • [Tagging] Bulk delete of multiple tags from Taxonomy Detail Page #130 (sometimes checkboxes are present, other times they're not)
• TBD: should the numbers next to each tag show the number of direct children or total the number of descendants? Currently we do # of children but that could be changed.
• Make sure the code for loading, filtering, and displaying the tags is clean and (where possible) shared between this page and the tag drawer. See discussions in the comments of FAL-3530.