This function returns the character that is currently used for background filling. This
character can be set using SetConsoleBackground(). Note that the character can also
be a special character composed by the MakeConsoleChr() function. To decompose such
characters into their constituents, you can call the DecomposeConsoleChr() function.
See DecomposeConsoleChr for details.
You must enable advanced console mode using EnableAdvancedConsole() before you
can use this function. See EnableAdvancedConsole for details.