Add 'w' and 's' bit to xarch instruction flags. (#61198)

Add 'w' and 's' bit to xarch instruction flags. (#61198)

Change encodes 'w' and 's' in the insFlags struct and INS_FLAG
entry for xarch instruction table. In addition, add methods to check
check if this flag is set for an instruction, which allows to start
simplifying some of the various ad-hoc checks for these bits that were
previously done per-instruction throughout emitxarch.cpp.