Auto merge of #120835 - oli-obk:no_hir_coherence, r=cjgillot

Avoid accessing the HIR in the happy path of `coherent_trait`

Unfortunately the hir is still used in unsafety checks, and we do not have a way to avoid that. An impl's unsafety is not part of any query other than hir.

So this PR does not affect perf, but could still be considered a cleanup

Author: bors