Add HEDLEY_TYPEOF#57

I was pointed to your project from StackOverflow (commenter says you're his "fav project" 😄) as I was looking for well-tested preprocessor detection of `__typeof`. https://stackoverflow.com/questions/73848714/detect-if-a-c-compiler-supports-typeof-and-or-decltype I see you started working on `__typeof` support a few years ago, but never committed it to trunk: https://github.com/nemequ/hedley/commit/9c3e8420cdb1ce1f89fcf70f07281e92df176f98#diff-b01d6052731bb4f6e3cf6dfb281442574769d119caa48f61a422e05f9b540f8a Some caveats: - In C, `int i; __typeof((i))` is `int`. In C++, `decltype(i)` is `int` but `decltype((i))` is `int&`. Therefore, you'd either have to document that the C++ version must be used only on _identifiers_, or (better?) you'd have to `#define HEDLEY_TYPEOF(...) typename std::remove_ref<decltype(__VA_ARGS__)>::type`. - In GCC and Clang and EDG and also in C23 if I understand correctly, `const int ci = 1; __typeof(ci)` is `const int`, i.e., `__typeof` does not strip cv-qualifiers. On ChibiCC, `__typeof__(ci)` is `int`. - I noticed that ChibiCC supports `__typeof__` but not `__typeof`. Most compilers support both. - I noticed that VBCC "supports" `__typeof(x)`, but it's a builtin that returns an `int` value (1=char, 3=int, 6=float, etc.) instead of the GNU C version that yields a typename.