feat!: use vue 2.7 to provide composition api

[danielroe]

❓ 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

With the new Vue 2.7 release, we can drop @vue/composition-api and rely on the native Vue implementation. This should significantly improve stability by removing the need to alias vue/vue2-bridge/vue-demi implementations.

It also decreases build size by approximately 30kB.

👉 Migration

Ensure the following packages (if in your lockfile) are at least at the following versions:

vue-loader: ^15.10.0
vue-demi: ^0.13.1
vue: 2.7.0

You may need to remove your lockfile and reinstall to ensure that your vue packages are all at 2.7.0 and none remain at 2.6.14.

Please see the Vue 2.7 announcement for more information.

📝 Checklist

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