Documentation for `is_domain_type` and `is_exact_type` is incomplete

[fingolfin]

The documentation says:

is_domain_type(::Type{T}) where T <: NCRingElement
is_exact_type(::Type{T}) where T <: NCRingElement

Return true if the given ring element type can only belong to elements of an integral domain or exact ring respectively. (An exact ring is one whose elements are represented exactly in the system without approximation.)

But one can actually also call them on ring types, not just ring element types (and arguably that's the more natural version for is_domain_type at least). I think the documentation should list those as well (and perhaps say that they are implemented by delegating to the element versions -- but that's really only important for implementors, so perhaps it can be in a callout / note