feat: Svelte support via Volar

[simonhaenisch]

Still work-in-progress, doesn't actually work yet (see failing test).

Would close #39.

[johnsoncodehk]

It seem getScriptSnapshot giving invalid svelte content.

<script ✂prettier:content✂="CgkJaW1wb3J0IEZvbyBmcm9tICcuL0Zvby5zdmVsdGUnOwoJCWltcG9ydCBCYXIgZnJvbSAnLi9CYXIuc3ZlbHRlJzsKCQlpbXBvcnQgVW51c2VkIGZyb20gJy4vVW51c2VkLnN2ZWx0ZSc7Cgk=">{}</script>

	<Foo />
	<Bar />

[johnsoncodehk]

If you need to debug, you can add breakpoint at node_modules/@volar/language-core/out/languageContext.js line 139.

[simonhaenisch]

It seem getScriptSnapshot giving invalid svelte content.

Actually, what you're seeing there is what Prettier passes to the plugin as code argument, and I'm assuming it comes from prettier-plugin-svelte. That base64 string is the encoded version of the script's actual value. Not very familiar with svelte tooling but I'll try to dig deeper when i find some more time for this.

Edit: this is what's doing this: https://github.com/sveltejs/prettier-plugin-svelte/blob/master/src/lib/snipTagContent.ts. I guess I could manually call that unsnipContent function that's exported there, just wondering whether it's a good approach 🤔