Make code NativeAOT compatible

[kant2002]

I know that C# files are autogenerated, but in case somebody what to use it without waiting for change in code gen tooling. This PR has 3 changes, all of them trivially can be updated in the codegen:

• Marshal.SizeOf(Type) switched to Marshal.SizeOf<T>()
• Marshal.PtrToStructure(IntPtr, Type) to Marshal.PtrToStructure<T>(IntPtr)
• Marshal.PtrToStructure<string>(IntPtr) is gross error, and should be mapped to Marshal.PtrToStringAnsi(IntPtr)

This and #707 should make life of C# developer, amenable and close #638 and #472.

[SupinePandora43]

Marshal.PtrToStructure<T>(IntPtr) can be replaced by *((T*)IntPtr)