Introduce PostDominanceInfo, fix properlyDominates() for Instructions

- introduce PostDominanceInfo in the right/complete way and use that for post
  dominance check in store-load forwarding
- replace all uses of Analysis/Utils::dominates/properlyDominates with
  DominanceInfo::dominates/properlyDominates
- drop all redundant copies of dominance methods in Analysis/Utils/
- in pipeline-data-transfer, replace dominates call with a much less expensive
  check; similarly, substitute dominates() in checkMemRefAccessDependence with
  a simpler check suitable for that context
- fix a bug in properlyDominates
- improve doc for 'for' instruction 'body'

PiperOrigin-RevId: 227320507