fix: Fix support for Svelte 5 snippet blocks

[SkylerLipthay]

Improves upon #68. I was happy to see that PR, but markup_fmt v0.15.1 still had problems with parsing Svelte 5 snippet blocks when used in combination with typescript 0.93.1:

Unexpected token `/`. Expected identifier, string literal, numeric literal or [ for the computed key at file:///...MyComponent.svelte#.tsx:352:10

        <>{/snippet}</>

I didn't investigate the problem carefully, but I think this has something to do with the fact that the parser was treating the closing {/snippet} tag as text instead of consuming it and re-emitting it in the printer. Maybe this was intentional, since copying the above {/key} parsing logic was the obvious move I did. Perhaps @bartlomieju could comment.

This PR also fixes a typo (ExpectSvelteIfBlock -> ExpectSvelteSnippetBlock) that improves error reporting.

[bartlomieju]

Perhaps @bartlomieju could comment.

I guess it wasn't intentional and that's a good catch.

[g-plane]

Thanks!