[clang] [Clang] Update value for __cpp_implicit_move (#84216) (PR #84228)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

[This page](https://clang.llvm.org/cxx_status.html) still refers to [P2266R1](https://wg21.link/p2266r1) but the approved revision is [P2266R3](https://wg21.link/p2266r3). Should we fix the citation in this PR or another?

https://github.com/llvm/llvm-project/pull/84228