[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.gradle

@@ -96,7 +96,6 @@ doxygen.sourceSets.main {
         exclude 'wpi/util/ErrorHandling.hpp'
         exclude 'wpi/util/SmallVector.hpp'
         exclude 'wpi/util/StringExtras.hpp'
-        exclude 'wpi/util/bit.hpp'
         exclude 'wpi/util/raw_ostream.hpp'
 
         // Sleipnir