Fix order and types of members in C++17 insert_return_type structs

Fix order and types of members in C++17 insert_return_type structs

	PR libstdc++/80761
	* include/bits/node_handle.h (_Node_insert_return): Reorder members.
	(tuple_size, tuple_element): Remove partial specializations.
	* include/bits/stl_tree.h (_Rb_tree::insert_return_type): Use
	const_iterator for std::set.
	* testsuite/23_containers/map/modifiers/extract.cc: New.
	* testsuite/23_containers/set/modifiers/extract.cc: New.
	* testsuite/23_containers/unordered_map/modifiers/extract.cc: New.
	* testsuite/23_containers/unordered_set/modifiers/extract.cc: New.

From-SVN: r248062