The Uses in foldShuffleToIdentity is intended to detect where an operand
is used to distinguish between splats, identities and concats of the
same value. When looking through multiple unsimplified shuffles the same
Use could be both a splat and a identity though. This patch changes the
Use to a Value and an original Use, so that even if we are looking
through multiple vectors we recognise the splat vs identity vs concat of
each use correctly.
Fixes#180338
fd40c60665