[libc++] Implement P1169R4 (static operator())

Reviewed By: ldionne, huixie90, #libc

Spies: EricWF, libcxx-commits, royjacobson

Differential Revision: https://reviews.llvm.org/D135016

NOKEYCHECK=True
GitOrigin-RevId: 3ec6c997c67d685c533b8c9c2cffde31d834b821
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 2b16ec5..3929be5 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -49,6 +49,7 @@
 - P2438R2 - ``std::string::substr() &&``
 - P0600R1 - ``nodiscard`` in the library
 - P0339R6 - ``polymorphic_allocator<>`` as a vocabulary type
+- P1169R4 - ``static operator()``
 
 Improvements and New Features
 -----------------------------