Allow GVN to produce places and not just locals. That may be too big of a hammer, as we may introduce new deref projections (possible UB footgun + probably not good for perf). The second commit opts out of introducing projections that don't have a stable offset, which is probably what we want. Hence no new Deref and no new Index projections. Fixes https://github.com/rust-lang/rust/issues/138936 cc `@scottmcm` `@dianqk`