Blender Git Loki

Revert "Fix entering edit-mode when object mode and edit-data don't match"

Before this change, object-data could only have
one of the objects referencing it in edit-mode.

Reverting since multiple meshes in edit-mode (for the same object data)
isn't thread-safe as the evaluated edit-meshes are created in the
original edit-mesh, causing a crash updating the depsgraph
for linked duplicates, see: T86767.

While we could support this case, it's a bigger project without
significant benefits, so reinstate the limitation of only
allowing a single object to be in edit-mode for each object data.

This adds back the error from T85974 which caused an assertion
but didn't crash in release builds.

This reverts commit 2b60d7d09c51716e8d98834061c1a61ed6b96cf5.