add manual DevTool component type

packages/svelte/src/devtool/DevTool.svelte.d.ts

@@ -1,2 +1,9 @@
 // i'm here so type generation doesn't get mad
-// TODO do we need to type this?
+// TODO generate this file during type generation
+export default DevTool;
+type DevTool = {
+	$on?(type: string, callback: (e: any) => void): () => void;
+	$set?(props: $$ComponentProps): void;
+};
+declare const DevTool: import("svelte").Component<$$ComponentProps, {}, "">;
+