Problem: some queries using NAME_CONST(.. COLLATE ...)
lead to server crash due to failed type cast.

Fix: return the underlying item's type in case of
NAME_CONST(.. COLLATE ...) to avoid wrong casting.


mysql-test/r/func_misc.result:
  Fix for bug#42014: Crash, name_const with coll
    - test result.
mysql-test/t/func_misc.test:
  Fix for bug#42014: Crash, name_const with coll
    - test case.
sql/item.cc:
  Fix for bug#42014: Crash, name_const with coll
    - in case of NAME_CONST('name', 'value' COLLATE collation)
  Item_name_const::type() returns type of 'value' argument 
  to awoid wrong type casting of the Item_name_const items.