Interface function for elements to retrieve the face scheme

[Davknapp]

Feature request

Is your feature request related to a problem? Please describe.
Up until the introduction of the CRTP scheme we could look up the eclass_scheme of the face of an element. The way that schemes are build now this is not possible anymore, because schemes can be ordered in an arbitrary way.

Describe the solution or feature you'd like
A function in the interface of the schemes where for the element and a face-id we get the scheme_id of the face with the given face_id.
Something like this:

scheme_id
get_face_scheme_id (const scheme_id scheme_id, const int face)

I would also like to replace the tree_class argument with a strong_type, but this is out of this scope.

Describe alternatives you've considered
No alternatives considered.

Estimated priority
"Priority: high" Should be solved as soon as possible

Additional context
Add any other context or screenshots about the feature request here.

[Davknapp]

Split this issue into (at least) two.