[Bug libstdc++/106749] Implement C++23 library features

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106749
Bug 106749 depends on bug 106953, which changed state.

Bug 106953 Summary: C++23 add new headers for freestanding
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106953

           What    |Removed                     |Added
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             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |FIXED