A preparatory patch for MDEV-6566.

Adding a new virtual function MY_CHARSET_HANDLER::copy_abort().
Moving character set specific code into the correspoding implementations
(for simple, multi-byte and mbmaxlen>1 character sets).

strings/ctype-bin.c

@@ -548,7 +548,8 @@ static MY_CHARSET_HANDLER my_charset_handler=
   my_strntod_8bit,
   my_strtoll10_8bit,
   my_strntoull10rnd_8bit,
-  my_scan_8bit
+  my_scan_8bit,
+  my_copy_8bit,
 };