[libc++] Implement P1425R4 (Iterator pair constructors for std::stack and std::queue)

Implement P1425R4

Reviewed By: Quuxplusone, #libc, Mordante

Spies: Mordante, jloser, libcxx-commits, arichardson

Differential Revision: https://reviews.llvm.org/D115977

NOKEYCHECK=True
GitOrigin-RevId: f3aed3698185dd4a03b210a9d73be4dc1efc580f
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index 714ed80..40e7558 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -296,6 +296,8 @@
     ------------------------------------------------- -----------------
     **C++ 2b**
     -------------------------------------------------------------------
+    ``__cpp_lib_adaptor_iterator_pair_constructor``   ``202106L``
+    ------------------------------------------------- -----------------
     ``__cpp_lib_allocate_at_least``                   *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_associative_heterogeneous_erasure``   *unimplemented*