Allow CoordinateElement to be passed to built-in mesh generators

[jpdean]

Describe new/missing feature

Currently, you cannot pass the coordinate element to the built-in mesh generators e.g. create_box or create_rectangle etc.

This would be helpful when using tensor product elements, for example.

Suggested user interface

No response

[jorgensd]

I guess we need to be very careful with the verification, as we would need to ensure that the coordinate element is a first order lagrange element (so the only thing we could really send in is a tensor-ordering or similar flag to indicate what pre-determined first order element one should use.