Base.windowserror function to encapsulate Windows errors in SystemErrors

[stevengj]

While working on #30611, I noticed a need for a function like systemerror but for Windows errors that use GetLastError() instead of errno, in order to:

• Delay the cost of creating the formatted error string (with Libc.FormatMessage) until the error is actually displayed (if ever).
• Still use a SystemError exception type, so that the exception type is consistent across platforms. (The fact that it is a Windows exception is stored in the extrainfo field.)
• Encapsulate a common pattern to shorten the code.

Along the way, I found and fixed a bunch of apparent bugs — functions that were calling systemerror after Windows API calls that don't set errno. (These would have thrown a SystemError exception with errorshow function that confusingly prints "no error" or similar as the error message.)

The resulting Base.windowserror function is not exported.

[stevengj]

Yay, green CI!

[stevengj]

@tkelman, @StefanKarpinski, good to merge?

[stevengj]

Note that libuv has a uv_translate_sys_error function that translates a Windows error code like ERROR_NOACCESS into a libuv error code like UV_EACCES. If there is another function to translate libuv error codes into errno error codes, we might use this to set the errno field of the SystemError to a useful value in windowserror, in case any caller wants to make use of this in a catch block.

[StefanKarpinski]

I guess my only question is whether this needs to be a separate function from systemerror or if we can just have a single function that plays both roles by looking at GetLastError and errno but it seems like there may be no way of doing that and one needs to know which one each Windows API call sets and correspondingly which of systemerror and windowserror one needs to call.

[stevengj]

I think they need to be separate functions, because whether you call GetLastError or errno depends on the preceding ccall. (Windows API calls generally need GetLastError and POSIX calls need errno.)