Add support for RMB/Escape canceling layer drag reordering in the Layers panel (#3426)

* Add support for RMB/Escape canceling layer drag reordering in the Layers panel

* Disable hover effects on layers during drag; fix insertion line getting cut off at top of stack

frontend/src/io-managers/drag.ts

@@ -1,24 +0,0 @@
-let draggingElement: HTMLElement | undefined;
-
-export function createDragManager(): () => void {
-	const clearDraggingElement = () => {
-		draggingElement = undefined;
-	};
-
-	// Add the event listener
-	document.addEventListener("drop", clearDraggingElement);
-
-	// Return the destructor
-	return () => {
-		// We use setTimeout to sequence this drop after any potential users in the current call stack progression, since this will begin in an entirely new call stack later
-		setTimeout(() => document.removeEventListener("drop", clearDraggingElement), 0);
-	};
-}
-
-export function beginDraggingElement(element: HTMLElement) {
-	draggingElement = element;
-}
-
-export function currentDraggingElement(): HTMLElement | undefined {
-	return draggingElement;
-}