Perf: slightly faster getShapeAtPoint (#3416)

This PR makes a small improvement to the speed of `getShapeAtPoint`. It
removes `Editor.getCurrentPageRenderingShapesSorted`.

### Change Type

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

packages/utils/src/lib/perf.ts

@@ -20,3 +20,31 @@ export function measureDuration(_target: any, propertyKey: string, descriptor: P
 	}
 	return descriptor
 }
+
+const averages = new Map<any, { total: number; count: number }>()
+
+/** @internal */
+export function measureAverageDuration(
+	_target: any,
+	propertyKey: string,
+	descriptor: PropertyDescriptor
+) {
+	const originalMethod = descriptor.value
+	descriptor.value = function (...args: any[]) {
+		const start = performance.now()
+		const result = originalMethod.apply(this, args)
+		const end = performance.now()
+		const value = averages.get(descriptor.value)!
+		const length = end - start
+		const total = value.total + length
+		const count = value.count + 1
+		averages.set(descriptor.value, { total, count })
+		// eslint-disable-next-line no-console
+		console.log(
+			`${propertyKey} took ${(end - start).toFixed(2)}ms | average ${(total / count).toFixed(2)}ms`
+		)
+		return result
+	}
+	averages.set(descriptor.value, { total: 0, count: 0 })
+	return descriptor
+}