Intrinsic type extension member signatures are erased

[auduchinok]

Consider signature file:

namespace ExtensionParts

type T =
    new: unit -> T

type T with
    member Foo: int
 

It's being formatted to the following with extension member signature being erased:

namespace ExtensionParts

type T =
    new : unit -> T

type T

Format config:

Parsing options:

[nojaf]

Repro: https://jindraivanek.gitlab.io/fantomas-ui/#?code=HYQwtgpgzgDiDGEAEBRAHgFwsKBLA9sAAogBOGUAsAFA0YCeMyAKkgLw1JdLAQDuALiQBXYLgxIAtAD4kzGnUYskfcQAtO3SGABGEUkgBi+fENzAMNIA&filename=C4WwDgdAZgzglkA