Canvas: Markdown links, copy to block, performance improvements

✨ Minor updates

Canvas now allows you to create links by writing out the markdown link syntax. Example: [sanity.io](https://sanity.io) -> sanity.io.

Various performance improvements to ensure Canvas uses less memory and can better handle larger documents.

It's now possible to link to specific blocks with the document body.

🐛 Notable bugfixes

Fixes an issue where making expanded text selections around lists wouldn't work as expected

Fixes an issue where lists wouldn't render correctly during continuation and AI output