Implement operator_pointer_diff::fold_range

prange has no default fold_range processing like irange does, so each
pointer specific operator needs to implement its own fold routine.

	PR tree-optimization/117222
	gcc/
	* range-op-ptr.cc (operator_pointer_diff::fold_range): New.
	(operator_pointer_diff::op1_op2_relation_effect): Remove irange
	variant.
	(operator_pointer_diff::update_bitmask): Likewise.

	gcc/testsuite
	* g++.dg/pr117222.C: New.