[clang] [Docs][Clang] Missing DR status for C++23-era papers in cxx_status.html (PR #68846)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

@Endilll Thanks for notification! P2280 was already handled, while P2156 was previously missed.
@cor3ntin I've add the DR status to P2156R1 and force-pushed.

https://github.com/llvm/llvm-project/pull/68846