fix: better error message for parse failures

[benmccann]

Description

Add enough details to allow diagnosing parse failures. Right now, the error message is just Unexpected token (6:132), but there's no clue as to what file or code that occurs in, so is impossible to debug

Additional context

I've had a long-running project to covert svelte.dev over to SvelteKit. This is one of the current blocking issues. Improving this error message helped us track the down the root cause as another Vite bug: #3304

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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