Remove PointerSize and use nint/nuint

[amerkoleci]

Hi @andrew-boyarshin ,
Recent .NET language added nint and nuint support, I would suggest to remove PointerSize and map to those directly, same applies to SharpGen.Runtime.COM.

It is supported in ClangSharp as well:
intptr_t -> nint
ptrdiff_t -> nint
size_t -> nuint
uintptr_t -> nuint
SIZE_T -> nuint
SSIZE_T -> nint

[andrew-boyarshin]

Having PointerSize might theoretically enable us to provide APIs not available on pre-.NET5 runtimes (like IComparable). But yeah, using these is simpler.

[amerkoleci]

Not sure what you mean, nuint maps to UIntPtr and nint maps to IntrPtr, so there is no special magin under the hood.

[amerkoleci]

If you plan to keep PointerSize then we need UPointerSize with ulong and map SIZE_T to that instance.
Otherwise we'll end in marshalling issues (amerkoleci/Vortice.Windows#185)

[andrew-boyarshin]

Yeah, I know that nint is a syntax sugar for System.IntPtr and native int. But until .NET 5 (dotnet/runtime#307) IntPtr had a much more narrow API surface, and so does the nint on these older runtimes.