Structures without postfixes try wide variant if not found in metadata

[StephenCleary]

Just using this project for the first time. I wanted to generate STARTUPINFOEX for use with CreateProcess.

In a new .NET Core 5 class library, I can specify CreateProcess in NativeMethods.txt, but I can't specify STARTUPINFOEX. After research, it turns out the metadata does have that structure, but with a W postfix. Specifying STARTUPINFOEXW in NativeMethods.txt does work.

CsWin32 will auto-append W to CreateProcess, but doesn't do it for STARTUPINFOEX. I assume CsWin32 does this for methods but not structures.

Is it possible to append W for structures automatically? If not, could you describe why not (just for my curiosity) and add a brief line to the getting-started docs (for future devs)?

[AArnott]

I don't recall a particular reason we couldn't do it for structures as well.

[AArnott]

CreateProcess actually generates a method called CreateProcess, although it binds to a CreateProcessW native method. So accepting CreateProcess as input doesn't produce a usability issue because you ask for X and you get X.
However for structs, which are types rather than methods and can be referenced elsewhere, we figured we should keep the original suffix on the name. Accepting STARTUPINFOEX as input but generating STARTUPINFOEXW may hurt usability.

Instead, I'm leaning with what we currently have, as described in #196, which at least helps folks discover and correct the problem:

warning PInvoke001: Method, type or constant "STARTUPINFOEX" not found. Did you mean "STARTUPINFOEXA" or "STARTUPINFOEXW"?