Create interface drops attributes in front of type declarations #9095

Create interface (the editor's "Create interface file" command) drops attributes written in front of a type declaration:

@tag("kind") type tagged = A(int)

gives

             type tagged = A(int)

The type declaration is copied from the source starting at its location, which begins at type, after the attributes in front of it, so they are replaced by spaces. For @tag (and likewise @unboxed and other representation attributes) the generated .resi then no longer matches the implementation, because the signature check compares the variant's tag name.

This happens without any functor involved, also on master. Found while reviewing #9077, part of #9074.