[X86] getFauxShuffleMask - OR(BITCAST(SHUFFLE()),BITCAST(SHUFFLE())) patterns should return bitcasted source values (#134993)
Noticed while investigating #133947 regressions - if we peek through
bitcasts we can lose track of oneuse/combined nodes in shuffle combining
Currently the same codegen as combineX86ShufflesRecursively still peeks
through the bitcasts itself, but we will soon handle this consistently
as another part of #133947