fix(appendToBody) use vue built-in Teleport

[s-montigny-desautels]

The teleport component will move the menu to the body and do a proper cleanup. We could also expose the "to" props to be configurable by the end user.

It was not a problem with vue-router per-say, but more a problem when the component was unmounted.

fix #1294

[andrewnorell]

I would love for the teleport "to" prop to be exposed and configurable

[greendrake]

I suggest this alternative approach: https://github.com/sagalbot/vue-select/pull/1775