Change Unicode xxx_general_ci and xxx_bin collation implementation to "inline" style

This task is similar to MDEV-17474, but for general_ci and _bin collations.

The current implementation my_strnxfrm_unicode_internal() has some bottlenecks:

• it uses cs->cset->mb_wc() virtual calls
• it accesses to cs->state and cs->caseinfo

We'll change the code by adding new strnxfrm-family function templates into strings/strcoll.ic.
Functions my_strnxfrm_unicode_internal(), my_strnxfrm_unicode(), my_strnxfrm_unicode_nopad() will migrate from strings/ctype-utf8.c to such function templates in strings/strcoll.ic.

Every collation will include strings/strcoll.ic and pass specific parameters, such as mb_wc() and UNICASE data related.

Additionally, we'll add fast paths for ASCII data.

After these changes, the template instantiation (e.g. for utf8_general_ci) will look like this:

#define MY_FUNCTION_NAME(x)      my_ ## x ## _utf8_general_ci

#define DEFINE_STRNXFRM_UNICODE

#define DEFINE_STRNXFRM_UNICODE_NOPAD

#define MY_MB_WC(cs, pwc, s, e)  my_mb_wc_utf8mb3_quick(pwc, s, e)

#define OPTIMIZE_ASCII           1

#define UNICASE_MAXCHAR          MY_UNICASE_INFO_DEFAULT_MAXCHAR

#define UNICASE_PAGE0            my_unicase_default_page00

#define UNICASE_PAGES            my_unicase_default_pages

...

#include "strcoll.ic"

The template included in this example will:

• use my_mb_wc_utf8mb3_quick() directly (inline or at least statically), instead of a virtual call.
• use MY_UNICASE_INFO_DEFAULT_MAXCHAR, my_unicase_default_page00, my_unicase_default_pages directly, without dereferencing members of CHARSET_INFO.
• enable fast path for ASCII