feat: rewrite public UI component rendering using tunnels (#6117)

* feat: rewrite public UI component rendering using tunnels

* factor out into components

* comments

* fix variable naming

* fix not hiding welcomeScreen

* factor out AppFooter and memoize components

* remove `UIOptions.welcomeScreen` and render only from host app

* factor out tunnels into own file

* update changelog. Keep `UIOptions.welcomeScreen` as deprecated

* update changelog

* lint

---------

Co-authored-by: Aakansha Doshi <aakansha1216@gmail.com>

src/components/hoc/withInternalFallback.tsx

@@ -0,0 +1,50 @@
+import { atom, useAtom } from "jotai";
+import React, { useLayoutEffect } from "react";
+
+export const withInternalFallback = <P,>(
+  componentName: string,
+  Component: React.FC<P>,
+) => {
+  const counterAtom = atom(0);
+  // flag set on initial render to tell the fallback component to skip the
+  // render until mount counter are initialized. This is because the counter
+  // is initialized in an effect, and thus we could end rendering both
+  // components at the same time until counter is initialized.
+  let preferHost = false;
+
+  const WrapperComponent: React.FC<
+    P & {
+      __fallback?: boolean;
+    }
+  > = (props) => {
+    const [counter, setCounter] = useAtom(counterAtom);
+
+    useLayoutEffect(() => {
+      setCounter((counter) => counter + 1);
+      return () => {
+        setCounter((counter) => counter - 1);
+      };
+    }, [setCounter]);
+
+    if (!props.__fallback) {
+      preferHost = true;
+    }
+
+    // ensure we don't render fallback and host components at the same time
+    if (
+      // either before the counters are initialized
+      (!counter && props.__fallback && preferHost) ||
+      // or after the counters are initialized, and both are rendered
+      // (this is the default when host renders as well)
+      (counter > 1 && props.__fallback)
+    ) {
+      return null;
+    }
+
+    return <Component {...props} />;
+  };
+
+  WrapperComponent.displayName = componentName;
+
+  return WrapperComponent;
+};