As part of this ticket, implement the aggregation expression for $encStrEndsWith.

As outlined in the design , ExpressionEncStrEndsWith will inherit from the base class, ExpressionEncTextSearch. 

This goal of this task :

• Implement the minimal requirements to allow the expression to be parsed by query analysis and the server rewrites
  • Implement parse & serialize.
  • Implement type checking/constraint checking when parsing the operands.

class ExpressionEncStrEndsWith : public ExpressionEncTextSearch {
public:    
Value evaluate(...) const final;    
Value serialize(...) const final;    
const char* getOpName() const;
static boost::intrusive_ptr<Expression> parse(...);

void acceptVisitor(ExpressionMutableVisitor* visitor) final;
void acceptVisitor(ExpressionConstVisitor* visitor) const final;
};