Merge pull request #62316 from apple/egorzhdan/cxxstdlib-step3

[cxx-interop] Replace `std` module name with the new spelling `CxxStdlib` in the overlay

Author: egorzhdan

stdlib/public/Cxx/std/std.swift

@@ -10,5 +10,5 @@
 //
 //===----------------------------------------------------------------------===//
 
-@_exported import std // Clang module
+@_exported import CxxStdlib // Clang module
 @_exported import Cxx // Swift module