Single-object viewer POC (#14)

This commit implements a Sketchfab-style single-object viewer as a minimal
proof-of-concept.

### `@storyteller/studio-web`
This is a new package to house web components for interfacing with the
`@storyteller/studio` WASM library. It currently includes a single component,
`<sts-viewer />`, which is exported from `@storyteller/studio-web/viewer`.

### `react-frontend`
This is a new application intended as a proof-of-concept and testbed for React
interop with `@storyteller/studio-web`.

Web components are currently a little bit fiddly to use in a React application.
`react-frontend/src/app/studio-viewer.tsx` demonstrates how a React-idiomatic
component can be written as a thin wrapper around a web component, and
`react-frontend/src/app/app.tsx` demonstrates that wrapper component in use.

react-frontend/src/app/studio-viewer.tsx

@@ -0,0 +1,46 @@
+import type { SceneStateEvent } from "@storyteller/studio";
+import { ViewerElement } from "@storyteller/studio-web/viewer";
+import "@storyteller/studio-web/viewer";
+import { MutableRefObject, forwardRef, useEffect, useRef } from "react";
+
+export interface Props {
+	objectId: string;
+	skyboxId: string;
+	onSceneStateChange?(event: SceneStateEvent): void;
+}
+
+export default forwardRef<ViewerElement, Props>(({
+	objectId,
+	skyboxId,
+	onSceneStateChange,
+}, ref) => {
+	const viewerRef = useRef<ViewerElement>(null);
+
+	useEffect(() => {
+		const viewer = viewerRef.current;
+
+		if (viewer && onSceneStateChange) {
+			viewer.addEventListener("scene-state", onSceneStateChange);
+			return () => {
+				viewer.removeEventListener("scene-state", onSceneStateChange);
+			}
+		}
+	}, [ref]);
+
+	const refCallback = (viewer: ViewerElement) => {
+		(viewerRef as MutableRefObject<ViewerElement>).current = viewer;
+
+		if (typeof ref === "function")
+			ref(viewer);
+		else if (ref != null)
+			ref.current = viewer;
+	}
+
+	return (
+		<sts-viewer
+			ref={refCallback}
+			objectId={objectId}
+			skyboxId={skyboxId}
+		/>
+	);
+});