Use loc::toupper_ch instead of SDL_toupper in VFormat

This commit is part of rewritten history of the localization branch.
The original (unsquashed) commit history can be found here:
https://github.com/Dav999-v/VVVVVV/tree/localization-orig

desktop_version/src/CWrappers.h

@@ -2,5 +2,6 @@
 #define CWRAPPERS_H
 
 char* HELP_number_words(int _t);
+uint32_t LOC_toupper_ch(uint32_t ch);
 
 #endif /* CWRAPPERS_H */