Blender Git Loki

Depsgraph: remove redundant mesh data duplication in edit-mode

This resolves a bottleneck where every update while transforming
copied the entire mesh data-block, which isn't needed as the edit-mesh
is the source of the data being edited.

Testing shows a significant overall speedup when transforming:

- ~1.5x with a subdivided cube 1.5 million vertices.
- ~3.0x with the spring mesh (edit-mode with modifiers disabled,
duplicated 10x to drop performance).

Reviewed By: sergey

Ref D11337