feat: support shiki twoslash

[antfu]

This PR allows the highlighter to use https://github.com/antfu/shikiji/tree/main/packages/shikiji-twoslash to render TypeScript code snippets with type information.

TODO:

• https://github.com/antfu/twoslash-cdn supports to pass an unstorage instance to cache the fetched .d.ts files across builds. But not sure how we could pass the options and instance for users to configure. Maybe a mdc.storage object like Nitro?
• Find a way to have TwoSlash hover display even outside of the code block with overflow: hidden - This is more like a styling issue and general to Shikiji. It's non-blocking, I'll try to experiment in parallel.

Preview:

[antfu]

#124 might be a better solution as it would allow users to do it on the userland

[antfu]

Close in favor of #129, later I will make a module to integrate twoslash for nuxt/content and MDC