[playground] fix: don't show compilation spinner when toggling dark mode

[JennyPng]

I noticed the playground compilation spinner appears when the dark mode toggle is clicked, which doesn't seem desirable

• When the dark mode toggle fires, WebsitePlayground re-renders and recreates imports (from .filter()) and importConfig ({ useShim: true }) as new object references

• These are dependencies of the useEffect in useStandalonePlaygroundContext in standalone.tsx, which re-runs the entire host creation and triggers the compile effect. So memoizing these to avoid that

• change to base-layout is because I noticed if I have dark mode, when switching pages, it briefly flashes to light mode before switching back to dark mode

[azure-sdk]

You can try these changes here

🛝 Playground	🌐 Website	🛝 VSCode Extension

[github-actions]

No changes needing a change description found.