Manipulator: modal callback can now cancel & pass events

Re-use operator return flags for manipulator modal & invoke,
this means manipulators can allow navigation or other events to be
handled as they run - see T52499

source/blender/editors/transform/transform_manipulator.c

@@ -1139,7 +1139,7 @@ static ManipulatorGroup *manipulatorgroup_init(wmManipulatorGroup *mgroup)
 /**
  * Custom handler for manipulator widgets
  */
-static void manipulator_modal(
+static int manipulator_modal(
         bContext *C, wmManipulator *widget, const wmEvent *UNUSED(event),
         eWM_ManipulatorTweak UNUSED(tweak_flag))
 {
@@ -1154,6 +1154,8 @@ static void manipulator_modal(
 	}
 
 	ED_region_tag_redraw(ar);
+
+	return OPERATOR_RUNNING_MODAL;
 }
 
 static void WIDGETGROUP_manipulator_setup(const bContext *UNUSED(C), wmManipulatorGroup *mgroup)

source/blender/editors/transform/transform_manipulator2d.c

@@ -167,7 +167,7 @@ BLI_INLINE void manipulator2d_origin_to_region(ARegion *ar, float *r_origin)
 /**
  * Custom handler for manipulator widgets
  */
-static void manipulator2d_modal(
+static int manipulator2d_modal(
         bContext *C, wmManipulator *widget, const wmEvent *UNUSED(event),
         eWM_ManipulatorTweak UNUSED(tweak_flag))
 {
@@ -179,6 +179,8 @@ static void manipulator2d_modal(
 	WM_manipulator_set_matrix_location(widget, origin);
 
 	ED_region_tag_redraw(ar);
+
+	return OPERATOR_RUNNING_MODAL;
 }
 
 void ED_widgetgroup_manipulator2d_setup(const bContext *UNUSED(C), wmManipulatorGroup *mgroup)