Fixes#123612, #123611, #123621
Continue the restructuring in previous commits in this area to avoid
repeating more work for every node. The commit is large for a bug fix
but the best way to fix the issues was to continue making the area more
generally sane. Some specific changes:
- Run the switch for undo type outside of the iteration over nodes.
- Further split multires and base mesh undo so they don't go through
the same per-node functions.
- Replace the node-tagging mechanism with specific loops per undo type.
- Properly assign the step type when pushing a single node at a time.
59d84a4c42