[libc++] Implement P2417R2 (A more constexpr bitset)

Reviewed By: ldionne, #libc

Spies: jloser, arichardson, libcxx-commits, arphaman

Differential Revision: https://reviews.llvm.org/D131218

NOKEYCHECK=True
GitOrigin-RevId: f02120fba28f2352fd9396683892fc6671caa137
diff --git a/docs/FeatureTestMacroTable.rst b/docs/FeatureTestMacroTable.rst
index e5a06dc..0ffd44d 100644
--- a/docs/FeatureTestMacroTable.rst
+++ b/docs/FeatureTestMacroTable.rst
@@ -308,6 +308,8 @@
     ------------------------------------------------- -----------------
     ``__cpp_lib_byteswap``                            ``202110L``
     ------------------------------------------------- -----------------
+    ``__cpp_lib_constexpr_bitset``                    ``202207L``
+    ------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_cmath``                     *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_typeinfo``                  *unimplemented*