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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> 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?

I think eventually I'd like to split out optional annexes and TSes to a separate table so we can track whether they're available in Clang or not rather than whether we conform or not. But for right now, I'd say let's stick with `No` because it's clear that we don't support them rather than N/A which somewhat implies that we don't need to make compiler changes to support them.

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