P0458R2 Checking for Existence of an Element in Associative Containers

P0458R2 Checking for Existence of an Element in Associative Containers

	* include/bits/stl_map.h (map::contains): Add for C++2a.
	* include/bits/stl_multimap.h (multimap::contains): Likewise.
	* include/bits/stl_multiset.h (multiset::contains): Likewise.
	* include/bits/stl_set.h (set::contains): Likewise.
	* include/bits/stl_tree.h (__has_is_transparent_t): Define alias.
	(_Rb_tree::_M_find_tr, _Rb_tree::_M_count_tr)
	(_Rb_tree::_M_lower_bound_tr, _Rb_tree::_M_upper_bound_tr)
	(_Rb_tree::_M_equal_range_tr): Use __has_is_transparent_t.
	* include/bits/unordered_map.h (unordered_map::contains)
	(unordered_multimap::contains): Add for C++2a.
	* include/bits/unordered_set.h (unordered_set::contains)
	(unordered_multiset::contains): Likewise.
	* testsuite/23_containers/map/operations/contains.cc: New.
	* testsuite/23_containers/multimap/operations/contains.cc: New.
	* testsuite/23_containers/multiset/operations/contains.cc: New.
	* testsuite/23_containers/set/operations/contains.cc: New.
	* testsuite/23_containers/unordered_map/operations/contains.cc: New.
	* testsuite/23_containers/unordered_multimap/operations/contains.cc:
	New.
	* testsuite/23_containers/unordered_multiset/operations/contains.cc:
	New.
	* testsuite/23_containers/unordered_set/operations/contains.cc: New.

From-SVN: r262418