Implement dumping

Implement dumping

This patch implements the dumping methods for tuple_holding_operation.
A number of overloads are used.  Note that no default case is given.
This approach makes it simple to detect when a new overload is needed
-- compilation will fail.  (There is an example of this in a later
patch in the series.)

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expprint.c (expr::dump_for_expression): New functions.
	* expop.h (dump_for_expression): New overloads.
	(tuple_holding_operation::dump, tuple_holding_operation::do_dump):
	Update.