Format `System.IntPtr` and `System.UIntPtr` as C# 9 keywords `nint` and `nuint`?

[stakx]

This isn't as clear-cut as it may be, since System.IntPtr has traditionally been used in interop scenarios to represent unmanaged pointers outside of unsafe contexts. nint "feels" much closer to a regular integral type than it does to void*, so I'm not sure if we should throw those two types in the same basket as all the other primitive types.

[pmg23]

I am in favour of returning nint and nuint in default mode, with NoKeywords mode opting out.