No user visible changes expected.
Needed for the asset shelf (#102879).
Adds a UI operator triggered on Ctrl+F that will attempt to start
filtering for the hovered UI view, typically enabling a filter text
button.
View items can implement their own filter method, there's no default
one. Maybe we should add default or re-usable string filtering method
though.
Filtering is applied after constructing the view and filtered out (as
in, invisible) items are kept in storage, so that their state
(selection, active, etc.) is preserved. The filtered state is cached in
the item, so this is only done once per redraw.
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