Remove dependency on `sveltedoc-parser`

[benmccann]

Describe the issue

I has nearly 100 dependencies (https://npmgraph.js.org/?q=sveltedoc-parser) and the last commit was 4 years ago (https://github.com/KatChaotic/sveltedoc-parser)

Describe the solution you'd like

It looks like our usage of sveltedoc-parser has really been reduced a lot. Going back through some history it seems like perhaps we now use it only to detect jsdoc comments on slots (#28492 (comment)) as demonstrated in KatChaotic/sveltedoc-parser#61. I have to say that I've never really seen this syntax get used in the wild and it's not something in the official Svelte docs as far as I know so it must be fairly rare. I think we could basically just drop support for it and very few people would miss it - especially with Svelte 5 replacing slots with snippets

Describe alternatives you've considered

Fork it or try to find some alternative

[JReinhold]

Yes it was always the plan to remove it in 9.0.

#28492 (comment)

Let's do it!