sql: replace flag MINMAX with flags MIN and MAX

Replaced sql function flag SQL_FUNC_MINMAX with couple new flags
SQL_FUNC_MIN and SQL_FUNC_MAX. This allows to distinguish MIN and
MAX function by flag instead of using user_data context.

This allows to delete user_data field in FundDef object in
further refactoring.

Needed for #2200, #4113, #2233