GPv3: Add "(De)select All" operator and keymap

This adds the `GREASE_PENCIL_OT_select_all` operator as well as a new keymap for edit mode for the new grease pencil objects.

Pull Request: https://projects.blender.org/blender/blender/pulls/108628

scripts/modules/bl_keymap_utils/keymap_hierarchy.py

@@ -68,7 +68,7 @@ _km_hierarchy = [
         ('Font', 'EMPTY', 'WINDOW', [
             _km_expand_from_toolsystem('VIEW_3D', 'EDIT_TEXT'),
         ]),
-
+        ('Grease Pencil', 'EMPTY', 'WINDOW', []),
         ('Pose', 'EMPTY', 'WINDOW', [
             _km_expand_from_toolsystem('VIEW_3D', 'POSE'),
         ]),