GPv3: Convert selection domain on curves when selection mode changes

When the selection mode in the Grease Pencil tool settings changes,
the selection domain of all curves in the active Grease Pencil object
has to change.
This PR handles that conversion. Point selections are converted to
curve selection and vice versa.

Note: this PR only takes care of selection modes 'Point' and 'Stroke'.
'Segment' mode is handled in a separate PR (#109221).

Pull Request: https://projects.blender.org/blender/blender/pulls/109964

scripts/startup/bl_ui/space_view3d.py

@@ -752,8 +752,18 @@ class VIEW3D_HT_header(Header):
             # Select mode for Editing
             if object_mode == 'EDIT':
                 row = layout.row(align=True)
-                row.prop_enum(tool_settings, "gpencil_selectmode_edit", text="", value='POINT')
-                row.prop_enum(tool_settings, "gpencil_selectmode_edit", text="", value='STROKE')
+                row.operator(
+                    "grease_pencil.set_selection_mode",
+                    text="",
+                    icon="GP_SELECT_POINTS",
+                    depress=(tool_settings.gpencil_selectmode_edit == 'POINT'),
+                ).mode = 'POINT'
+                row.operator(
+                    "grease_pencil.set_selection_mode",
+                    text="",
+                    icon="GP_SELECT_STROKES",
+                    depress=(tool_settings.gpencil_selectmode_edit == 'STROKE'),
+                ).mode = 'STROKE'
 
         # Grease Pencil (legacy)
         if obj and obj.type == 'GPENCIL' and context.gpencil_data: