CSharpTypePrinter: use type width to convert C++ types to C# types

We need to convert C++ integer types to C# types using the TargetInfo, as the
type bitwidths depend on the target architecture.

This fixes the main 64bit issue, which is that on 64bit Linux the current code
converts C++'s long to System.Int32, instead of System.Int64.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@iki.fi>