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

release/scripts/startup/bl_ui/properties_grease_pencil_common.py

@@ -759,6 +759,16 @@ class GreasePencilLayerAdjustmentsPanel:
         col = layout.row(align=True)
         col.prop(gpl, "lock_material")
 
+        # Transforms
+        row = layout.row(align=True)
+        row.prop(gpl, "location")
+
+        row = layout.row(align=True)
+        row.prop(gpl, "rotation")
+
+        row = layout.row(align=True)
+        row.prop(gpl, "scale")
+
 
 class GPENCIL_UL_masks(UIList):
     def draw_item(self, _context, layout, _data, item, icon, _active_data, _active_propname, _index):