fix: resolve issues in Runes mode detection causing parser malfunctions

[baseballyama]

Fixed: #633 (comment)

Before #633, the default value was set to true when it was unclear whether the file was in Runes mode. However, this approach could cause eslint-plugin-svelte to malfunction if the file was not in Runes mode. The behavior was changed to return undefined when the mode was uncertain to address this. Unfortunately, this caused issues in parts of the parser that rely on Runes. This PR fixes that bug.

I want to add a test for this, but I’m not sure how to do it. 😅
-> I added a test and I confirmed that this test is failed without changes.👍

[changeset-bot]

🦋 Changeset detected

Latest commit: 68abb47

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte-eslint-parser	Patch

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[pkg-pr-new]

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npm i https://pkg.pr.new/svelte-eslint-parser@638

commit: 68abb47

[coveralls]

Pull Request Test Coverage Report for Build 12742284310

Details

• 10 of 12 (83.33%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 94.744%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser/typescript/analyze/index.ts	4	6	66.67%

Totals
Change from base Build 12738544566:	0.02%
Covered Lines:	10330
Relevant Lines:	10780

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💛 - Coveralls

[baseballyama]

I’m merging this because, without this fix, a large number of lint errors could occur.