[IRBuilder] Generate nuw GEPs for struct member accesses (#99538)

Generate nuw GEPs for struct member accesses, as inbounds + non-negative
implies nuw.

Regression tests are updated using update scripts where possible, and by
find + replace where not.

GitOrigin-RevId: 94473f4db6a6f5f12d7c4081455b5b596094eac5