Theme Generator Shiki Component Improvements

[endigo9740]

We've currently implemented a code block for the new Theme Generator using Shiki. I've modeled this after the integration from the Floating UI Svelte app. However, Shiki has updated to use a Singleton approach. So we should update at least the Theme Generator implementation, which can be found in /lib/components/common/CodeBlock/CodeBlock.svelte

This will be used as the basis for the upcoming integration guide, so any other improvements are welcome:

• Integration: Code Blocks #2396

Likewise, I wouldn't mind if the Floating UI Svelte version was updated alongside this. But it's lesser priority.