Fix getAppTracking for Vue 3 support

[frandiox]

@Akryum In Vue 2's composition API, the instance has a vm.$root property with the root component.

However, in Vue 3, the property is called vm.root (without dollar).

With this small change I was able to upgrade a project using latest @vue/apollo-composable alpha to Vue 3.

[ivansieder]

@frandiox shouldn't this also be updated in @antfu's vue-demi? AFAIK the issue comes from a piece of code which uses vue-demi?

[frandiox]

@ivansieder I don't think vue-demi has anything to do here. It simply redirects to Vue 2 or Vue 3 conditionally. The problem is that Vue 2's composition API is not exactly the same as Vue 3.

I guess it could be possible to fix it in the composition API itself by aliasing root to $root and any other Vue internal change 🤔