Support JOINs wide-DECIMAL keys.

There are number of JOIN types and JOIN-based operations in MCS that doesn't support 16 byte wide-decimal columns as JOIN key parts.
Here is the list of JOIN and JOIN-based operations that must support wide-decimal:

• INNER JOIN
• LEFT|RIGHT JOIN
• [NOT]IN+correlated subquery
• [NOT] EXISTS
  The JOIN operation must support equi predicates with different width columns ,e.g. DECIMAL(38) = INT. The prerequisite for cross-type join is that both sides must be integers, e.g. DECIMAL(20) and BIGINT. It is impossible to join DECIMAL(20,1) and BIGINT.
  The JOIN operation must also support equi predicates functions with a wide-decimal argument.