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/object_quick_effects.py

@@ -73,9 +73,10 @@ class QuickFur(Operator):
             )
 
     def execute(self, context):
+        workspace = context.workspace
         fake_context = context.copy()
         mesh_objects = [obj for obj in context.selected_objects
-                        if obj.type == 'MESH' and obj.mode == 'OBJECT']
+                        if obj.type == 'MESH' and workspace.object_mode == 'OBJECT']
 
         if not mesh_objects:
             self.report({'ERROR'}, "Select at least one mesh object")