Codefix: Potential unterminated string returned from convert_to_fs.

Converting from UTF-8 to UTF-16 could have resulted in a buffer overflow if the buffer size was exactly the length of the converted string.

Pass string_view/span to convert_from/to_fs instead, and ensure the buffer is terminated. This replaces passing a pointer to the buffer and the buffer size as separate parameters, allowing the compiler to pass both in one parameter.

Removes use of `lengthof()`.

src/os/windows/string_uniscribe.cpp

@@ -147,7 +147,7 @@ static HFONT HFontFromFont(Font *font)
 	logfont.lfHeight = font->fc->GetHeight();
 	logfont.lfWeight = FW_NORMAL;
 	logfont.lfCharSet = DEFAULT_CHARSET;
-	convert_to_fs(font->fc->GetFontName(), logfont.lfFaceName, lengthof(logfont.lfFaceName));
+	convert_to_fs(font->fc->GetFontName(), logfont.lfFaceName);
 
 	return CreateFontIndirect(&logfont);
 }