feat: setup twoslash for codeblocks

[antfu]

This is working now, but with a few caveats:

Preview

Short-term

• twoslash is not stable yet: https://github.com/twoslashes/twoslash
• Using shikiji's beta https://shikiji.netlify.app/packages/twoslash, which is wait for twoslash
• Once shikiji v0.10 released and VitePress upgrade to it, the pnpm overrides can be removed

Long-term

• __VUE_OPTIONS_API__: true is required at this moment because floating-vue is still using Options API
• shamefully-hoist=true is required at this moment for twoslash to resolve the types correctly

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And later we need to revise code blocks across the docs to add the twoslash flag.

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[antfu]

I think it's ready now. The only thing is that if we should bring Options API or wait for Floating Vue to adopt to Composition API only

[NataliaTepluhina]

@antfu thank you for working on this! Looks great ✨

Could you please resolve the conflicts? I'll merge the PR and add twoslash to the codeblocks

[brc-dd]

I'll release vitepress by tomorrow. It will have shiki@v1. We can remove resolutions from package.json here.

Also, is it possible to use the older code background with twoslash? github-dark's default background doesn't look nice with other stuff.

[yyx990803]

Let's enable Options API then, it's ok for now until we have a version of floating-vue that is Composition API based.

[antfu]

Should be good to go now

[yyx990803]

I think we need to be a bit selective on where to use these, let me take a pass on the rest of the docs so it doesn't become distractive.