So far the Asset Browser just showed the same popups and settings as the
File Browser. Not all of them made sense for the Asset Browser though.
- Don't show inapplicable recursion toggle.
- Don't show sorting options, which don't work with assets anyway.
- Don't show the Filter popover, there are currently no applicable items in there.
Just like in D12057, I decided to add separate classes for the Asset
Browser case.