[playground] Extract shared components (#16819)

## Summary
Extract components that can be shared with the Red Knot playground.

## Test Plan

`npm start`

playground/shared/src/AstralButton.tsx

@@ -0,0 +1,36 @@
+import type { ButtonHTMLAttributes } from "react";
+import classNames from "classnames";
+
+export default function AstralButton({
+  className,
+  children,
+  ...otherProps
+}: ButtonHTMLAttributes<any>) {
+  return (
+    <button
+      className={classNames(
+        "uppercase",
+        "ease-in-out",
+        "font-heading",
+        "outline-radiate",
+        "transition-all duration-200",
+        "bg-radiate",
+        "text-black",
+        "hover:text-white",
+        "hover:bg-galaxy",
+        "outline-1",
+        "dark:outline",
+        "dark:hover:outline-white",
+        "rounded-md",
+        "tracking-[.08em]",
+        "text-sm",
+        "font-medium",
+        "enabled:hover:bg-galaxy",
+        className,
+      )}
+      {...otherProps}
+    >
+      {children}
+    </button>
+  );
+}