[DAGCombiner] Improve FMin/FMax DAGCombines (#161352)
Add several improvements to DAGCombine patterns for fmin/fmax:
* Fix incorrect results due to minimumnum not being marked as IsMin
- e.g. nnan minimumnum(x, +inf) returned +inf instead of x
* Fix incorrect results checking maximumnum for vecreduce patterns
* Make maxnum/minnum return QNaN if one input is SNaN instead of X
* Quiet SNaN inputs when propagating them e.g. maximum(x, SNaN) = QNaN
* Update comments to mark when SNaN propagation is being ignored
