Rollup merge of #152377 - Zalathar:active-job-guard, r=nnethercote

Rename the query system's `JobOwner` to `ActiveJobGuard`, and include `key_hash`

`JobOwner` appears to have had more responsibilities in the past, but nowadays it's just a stack-guard object used by `execute_job` to poison the query state for the current key if some inner part of query execution panics.

The new name and comments should hopefully be clearer about its (limited) role.

I have also included a follow-up change that stores both the key and its previously-computed hash in the guard, instead of just the key. This avoids having to pass the key to `complete`, and avoids having to recompute the hash in `drop`.

r? nnethercote (or compiler)

Author: matthiaskrgr