GPencil: Add new parameteres to transform layers

When using grease pencil for drawing Storyboards, it's very common to require a transform of the layers. This transform can be done using the offset modifier, but in some cases, the scene requires a lot of modifiers and makes the file hard to work.

This new feature adds a transforms Location, Rotation and Scale at Layer level, and allows to transform the layer without using a modifier, keeping the scene more clean.

{F9480695}

This feature was suggested by @pepeland after receiving feedback from several artists.

Also, done some code cleanup and rename some functions to get a better naming.

Maniphest Tasks: T83660

Differential Revision: https://developer.blender.org/D9761

source/blender/blenkernel/intern/object_update.c

@@ -225,7 +225,7 @@ void BKE_object_handle_data_update(Depsgraph *depsgraph, Scene *scene, Object *o
     case OB_GPENCIL: {
       BKE_gpencil_prepare_eval_data(depsgraph, scene, ob);
       BKE_gpencil_modifiers_calc(depsgraph, scene, ob);
-      BKE_gpencil_update_layer_parent(depsgraph, ob);
+      BKE_gpencil_update_layer_transforms(depsgraph, ob);
       break;
     }
     case OB_HAIR: