Add inpainting and outpainting to Imaginate (#864)

* Do not select layer immediatly on drag

* Add LayerReferenceInput MVP widget

* Properties Panel

* Fix dragging marker flicker

* Change mask shape to outline

* Add mask rendering

* Simplify select code

* Remove colours

* Fix inpaint/outpaint and rearrage widget UX

* Add mask blur and mask starting fill parameters

* Guard for the case when the layer is missing

* Add icon to LayerReferenceInput to finalize its UI

Co-authored-by: Keavon Chambers <keavon@keavon.com>

frontend/src/io-managers/drag.ts

@@ -0,0 +1,26 @@
+let draggingElement: HTMLElement | undefined;
+
+export function createDragManager(): () => void {
+	const clearDraggingElement = (): void => {
+		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): void {
+	draggingElement = element;
+}
+
+export function currentDraggingElement(): HTMLElement | undefined {
+	return draggingElement;
+}