strerror: Add Curl_winapi_strerror for Win API specific errors

strerror: Add Curl_winapi_strerror for Win API specific errors

- In all code call Curl_winapi_strerror instead of Curl_strerror when
  the error code is known to be from Windows GetLastError.

Curl_strerror prefers CRT error codes (errno) over Windows API error
codes (GetLastError) when the two overlap. When we know the error code
is from GetLastError it is more accurate to prefer the Windows API error
messages.

Reported-by: Richard Alcock
Fixes https://github.com/curl/curl/issues/4550
Closes https://github.com/curl/curl/pull/4581