This is a non-functional change and should not change the server behavior.

Casefolding information is now stored in items of a new data type MY_CASEFOLD_CHARACTER:

typedef struct casefold_info_char_t
{
  uint32 toupper;
  uint32 tolower;
} MY_CASEFOLD_CHARACTER;

Before this change, casefolding tables for Asian collations were stored in:

typedef struct unicase_info_char_st
{
  uint32 toupper;
  uint32 tolower;
  uint32 sort;
} MY_UNICASE_CHARACTER;

The "sort" member was not used in the code handling Asian collations,
it only wasted space.
(it's only used by Unicode _general_ci and _general_mysql500_ci collations).

Unicode collations (at least UCA and _bin) should also be refactored later,
but under terms of a separate task.