Add basic mouse support in code editor

mouse.ts

@@ -79,6 +79,10 @@ export const refreshMouse = () => {
 	mouseEvents.length = 0;
 }
 
+export const mouseDown = (button: number = M.LEFT) => {
+	return mouseEvents.some(ev => ev.button === button && ev.type === "down");
+}
+
 export const mouseClick = (button: number = M.LEFT) => {
 	return mouseEvents.some(ev => ev.button === button && ev.type === "click");
 }