Initial support for mobile devices (#787)

* Initial support for mobile devices

No editing yet, but UI looks nice and you can open the canvas menu

* Add support for editing shape color, etc

* Allow the mobile menus to cover the shape selector

* Hopefully fix test error

* Fix touch on canvas

* Fix safe area handling & remove unused Island

src/is-mobile.tsx

@@ -0,0 +1,25 @@
+import React, { useState, useEffect, useRef, useContext } from "react";
+
+const context = React.createContext(false);
+
+export function IsMobileProvider({ children }: { children: React.ReactNode }) {
+  const query = useRef<MediaQueryList>();
+  if (!query.current) {
+    query.current = window.matchMedia(
+      "(max-width: 600px), (max-height: 500px)",
+    );
+  }
+  const [isMobile, setMobile] = useState(query.current.matches);
+
+  useEffect(() => {
+    const handler = () => setMobile(query.current!.matches);
+    query.current!.addListener(handler);
+    return () => query.current!.removeListener(handler);
+  }, []);
+
+  return <context.Provider value={isMobile}>{children}</context.Provider>;
+}
+
+export default function useIsMobile() {
+  return useContext(context);
+}