[clang] [C23] Update status page for TS 18661 integration (PR #105693)

[Joshua Cranmer via cfe-commits]

https://github.com/jcranmer-intel commented:

It might be better to list most of these as "N/A" rather than "No", for the simple reason that decimal floating point is an optional feature we do not support. Or maybe just a footnote saying something to that effect?

https://github.com/llvm/llvm-project/pull/105693