Quick fix for adding lang="ts" attribute

[mquandalle]

Description

Sometimes we write typescript types in a <script> tag and get an error.

sveltejs/svelte#17070

Proposed solution

It would be nice to have a quick fix action to add the lang="ts" attribute

Alternatives

No response

Additional Information, eg. Screenshots

No response

[jasonlyu123]

It should be possible, but it might need to be something TypeScript can detect, like having a "xxx can only be used in TypeScript files" message. If it's an error from the Svelte compiler, it needs to have a clear message/code for us to detect. So at least for now, it won't fix the linked issue.