[wpiutil] Remove bit.hpp; replace with C++23 bit (#8792)

#7492 didn't catch all the uses and #7973 patched out byteswap in
Sleipnir for some reason (despite having upgraded compilers already)?

docs/BUILD.bazel

@@ -89,7 +89,6 @@ doxygen(
         "*/wpi/util/ErrorHandling.hpp",
         "*/wpi/util/SmallVector.hpp",
         "*/wpi/util/StringExtras.hpp",
-        "*/wpi/util/bit.hpp",
         "*/wpi/util/raw_ostream.hpp",
         # Sleipnir
         "*/sleipnir/optimization/solver/interior_point.hpp",