MDEV-8360 Clean-up CHARSET_INFO: strnncollsp: diff_if_only_endspace_difference

- Removing the "diff_if_only_endspace_difference" argument from
  MY_COLLATION_HANDLER::strnncollsp(), my_strnncollsp_simple(),
  as well as in the function template MY_FUNCTION_NAME(strnncollsp)
  in strcoll.ic

- Removing the "diff_if_only_space_different" from ha_compare_text(),
  hp_rec_key_cmp().

- Adding a new function my_strnncollsp_padspace_bin() and reusing
  it instead of duplicate code pieces in my_strnncollsp_8bit_bin(),
  my_strnncollsp_latin1_de(), my_strnncollsp_tis620(),
  my_strnncollsp_utf8_cs().

- Adding more tests for better coverage of the trailing space handling.

- Removing the unused definition of HA_END_SPACE_ARE_EQUAL

sql/strfunc.cc

@@ -337,7 +337,7 @@ int find_string_in_array(LEX_STRING * const haystack, LEX_STRING * const needle,
   const LEX_STRING *pos;
   for (pos= haystack; pos->str; pos++)
     if (!cs->coll->strnncollsp(cs, (uchar *) pos->str, pos->length,
-                               (uchar *) needle->str, needle->length, 0))
+                               (uchar *) needle->str, needle->length))
     {
       return (pos - haystack);
     }