fix: augment vue rather than @vue/runtime-core

[danielroe]

Description

In line with vuejs/router#2295 and nuxt/nuxt#28542, this moves to augment vue rather than @vue/runtime core.

This is now officially recommended in the docs and it must be done by all libraries or it will break types for other libraries.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Improvement/refactoring (non-breaking change that doesn't add any feature but make things better)

[m0ksem]

Thanks!