fix(nuxt): check before appending comma in composable keys

[danielroe]

🔗 Linked issue

resolves nuxt/nuxt#15272

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

We were previously not confirming whether there was a trailing comma before appending our own.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[pi0]

Perf: this is a heavy operation to run on each code block, copying the whole string, trimming (that also copies) to only check the last character is ,. We could replace it with a look-behind loop.

Suggested change

	const endsWithComma = code.slice(codeIndex + (node as any).start, codeIndex + (node as any).end - 1).trim().endsWith(',')
	// TODO: Optimize me (https://github.com/nuxt/framework/pull/8529)
	const endsWithComma = code.slice(codeIndex + (node as any).start, codeIndex + (node as any).end - 1).trim().endsWith(',')