Object Mode: move to workspace struct

- Read-only access can often use EvaluationContext.object_mode
- Write access to go to WorkSpace.object_mode.
- Some TODO's remain (marked as "TODO/OBMODE")
- Add-ons will need updating
  (context.active_object.mode -> context.workspace.object_mode)
- There will be small/medium issues that still need resolving
  this does work on a basic level though.

See D3037

release/scripts/startup/bl_operators/mesh.py

@@ -57,8 +57,9 @@ class MeshMirrorUV(Operator):
         precision = self.precision
         double_warn = 0
 
+        workspace = context.workspace
         ob = context.active_object
-        is_editmode = (ob.mode == 'EDIT')
+        is_editmode = (workspace.object_mode == 'EDIT')
         if is_editmode:
             bpy.ops.object.mode_set(mode='OBJECT', toggle=False)