feat: folding range support

[jasonlyu123]

#1704 #1120

This adds the syntactic folding range support instead of the VSCode's default indentation-based and regex-based folding. For embedded languages like Pug and Sass, I added a simplified version of indentation folding. The indentation folding is also a fallback for svelte blocks if there is a parser error.

For users who prefer the speed of the indent-based folding, You can still roll back with the following config.

{
    "[svelte]": {
        "editor.foldingStrategy": "indentation"
    }
}

Implementation

The commits might be messy because I started this nearly a year ago and have done part of this every few months 😆. The process is "the TypeScript result is good enough that's used it for HTML and svelte block as well" to "the TypeScrip result has a lot of weird cases, that's use HTML language service and svelte ast instead".

Now, the TypeScript folding handles everything inside the script tags and any folding ranges that are one-to-one in the generated code, i.e. it's untouched or only being moved around. Component tag and HTML tag are handled by HTML language service. Svelte blocks like each, if and await are extracted from Svelte AST. And folded from the end of the start tag to the start of the end tag. For example,

{#if hi}<!-- start here-->
  {hi}
<!-- end here-->{/if}

VSCode only supports line folding, so it'll start at line 0 and end at line 1, leaving line 2 visible after fold.

{#if hi}...
{/if}

[dummdidumm]

Damn, impressive work!

General thought: We're using various getText() operations like indexOf, split(/\n\r?/) etc in many places - maybe it's worth having some of these operations move into the document in a more performant manner (for example, keeping the splitted lines cached etc).

[Xeronic]

style?