Adds a column to the right in the Library Overrides Hierarchies view mode to toggle editability of library overrides. Note that making a library override non-editable currently involves clearing all overridden properties. This is an arguable design choice, we should probably at least warn the user before doing this. Part of T95802. Reviewed by: Bastien Montagne Differential Revision: https://developer.blender.org/D14653