first pass at dedicated bitmap tab view, & all the machinery of going from watch window w/ view rule -> dedicated ui

src/ui/ui_core.c

@@ -527,6 +527,12 @@ ui_dt(void)
 
 //- rjf: drag data
 
+internal Vec2F32
+ui_drag_start_mouse(void)
+{
+  return ui_state->drag_start_mouse;
+}
+
 internal Vec2F32
 ui_drag_delta(void)
 {