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

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.