MDEV-6855 Assertion `cond_type == Item::FUNC_ITEM' failed in check_group_min_max_predicates with GROUP BY, aggregate in WHERE SQ, multi-part key


mysql-test/r/group_by.result:
  Test for MDEV-6855
mysql-test/t/group_by.test:
  Test for MDEV-6855
sql/item.h:
  Fixed spelling error
sql/opt_range.cc:
  Added handling of cond_type == Item::CACHE_ITEM in WHERE clauses for MIN/MAX optimization.
  Fixed indentation