Currently replacing the Mesh during evaluation with the object info node
can cause us to use invalid original indices when the source object is
in edit mode. This is really a more fundamental problem though: we have
no way to tell whether an evaluated mesh actually corresponds to the
object's original mesh.
This commit changes to explicitly propagating the edit mesh pointer
through copied and changed meshes during modifier and nodes evaluation,
instead of just blindly copying the edit mode pointer from the original
mesh to the evaluated mesh. A benefit of not writing to the evaluated
mesh means it can be shared, potentially offering a future performance
improvement for uses of the object info node.
When we detect an invalid correspondence between the evaluated/original
meshes, we skip extracting the cage mesh's data and skip extracting edit
mesh data from the evaluated object.
This commit also moves the source of "object is in edit mode" truth in
the draw module from whether the evaluated mesh has an edit mode pointer
to the object's mode flag. That's a simplification that's also helpful
to reduce the strong linking between BMesh and edit mode.
Pull Request: https://projects.blender.org/blender/blender/pulls/120999
839108f623