Wide architecture: `nint`/`nuint` should become synonymous to `long`

[ForNeVeR]

Wide architecture set in Cesium supports same type sizes and layouts for any hardware platforms.

The only problem remaining is that it's not the same for nint / nuint: these types will currently compile to IntPtr and UIntPtr, platform-dependent.

We should improve the spec and make them synonymous to long and ulong on the wide architecture.