The previous commit introduced all the basic bits and pieces necessary
to support asset shelves as experimental feature, but didn't actually
add support for any specific editor. With this commit asset shelves can
be registered in 3D Views, which should soon be used by the Pose Library
add-on to replace its previous UI in the sidebar (see
blender/blender-addons#104546). Note that until then, there will still be no
actual asset shelf to display.
Also adds:
- Toggle to hide/unhide the asset shelf under "View" -> "Asset Shelf"
- 3D View theme settings for the asset shelf regions.
None of the changes are visible if the experimental option for the asset
shelf is not enabled.
Approved as part of #104831, then split off as separate commit.
Pull Request: #110767
8b19477e9c