Embedded languages in tagged templates

[abose]

Discussed in #762

^{Originally posted by aral December 17, 2022}
Just testing out Phoenix, possibly as a good tool for education when working on Kitten projects in the future, and it would be lovely to have syntax highlighting and language intelligence for embedded languages within tagged templates (as they’re used everywhere in it).

Specifically, for HTML and CSS:

const markup = html`
  <h1>I’m HTML</h1>
`
const styles = css`
   h1 { font-size: large; }
`

Haven’t looked into the code so I don’t know how easy/possible it is to implement but it seems like the typescript-language-server LSP is able to handle them at least (I’m using it in Helix Editor currently).