Implement the narrowType dispatcher.

The type narrowing logic for MatchExpression will be implemented in the type_system module.

The narrowType signature should be:

Type narrowType(Type inputType, const MatchExpression* expr, bool assumeTrue); 

We can implement this narrowType function using double-dispatch with a visitor, similar to exec::matcher::matches(..).

narrowType should use NarrowTypeMatchExpressionVisitor (or similar) which dispatches to a set of private narrowType overloads like:

Type narrowType(Type inputType, const TypeMatchExpression* expr, bool assumeTrue);

This will allow us to implement the type narrowing logic individually per MatchExpression type without touching the MatchExpression headers.