feat(Tabs): add before-change event

[alexovn]

❓ 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)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR introduces a new @before-change event for the Tabs component, allowing code execution before the @change event is triggered. This is useful in scenarios where data validation is required before switching tabs or when preventing (or resolving) the next @change event handling.

Under the hood, it uses a Promise object with the resolve() method, which is passed to the before-change event emitter. This allows it to be invoked when needed to resolve the next @change event handling.

Example: Verify that form data in a tab has been properly saved before switching to another tab, and display a confirmation window with a relevant message to users.

📝 Checklist

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

[pkg-pr-new]

npm i https://pkg.pr.new/@nuxt/ui@3493

commit: b1f6275