Perf: block hit tests while moving camera (#3418)

This PR uses an element that prevents hit tests on shapes while the
camera is moving.


https://github.com/tldraw/tldraw/assets/23072548/9905f3d4-ba64-4e4d-ae99-194f513eaac8

### Change Type

- [x] `sdk` — Changes the tldraw SDK
- [x] `improvement` — Improving existing features


### Test Plan

1. Move the camera.
2. Interact with the canvas.
3. Zoom in and out.

### Release Notes

- Improves performance of canvas while the camera is moving.

packages/editor/src/lib/components/default-components/DefaultCanvas.tsx

@@ -137,6 +137,7 @@ export function DefaultCanvas({ className }: TLCanvasComponentProps) {
 					</div>
 					<InFrontOfTheCanvasWrapper />
 				</div>
+				<MovingCameraHitTestBlocker />
 			</div>
 		</>
 	)
@@ -590,3 +591,16 @@ function InFrontOfTheCanvasWrapper() {
 	if (!InFrontOfTheCanvas) return null
 	return <InFrontOfTheCanvas />
 }
+
+function MovingCameraHitTestBlocker() {
+	const editor = useEditor()
+	const cameraState = useValue('camera state', () => editor.getCameraState(), [editor])
+
+	return (
+		<div
+			className={classNames('tl-hit-test-blocker', {
+				'tl-hit-test-blocker__hidden': cameraState === 'idle',
+			})}
+		/>
+	)
+}