Before this, we would build the sub-trees of some elements, just to
remove them afterwards. In big files, this would sometimes build ten
thousands of elements unnecessarily. Now support not building those
sub-trees in the first place.
Performance tests in a Sprite Fright production file (release build):
- View Layer display mode, reduced Outliner tree rebuilding from ~45ms
to 12-17ms
- Library Overrides display mode, Hierarchies view, reduced tree
rebuilding from 5-6s(!) to 220ms
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