Auto merge of #123126 - oli-obk:feed_crate_num, r=davidtwco

Enable `CrateNum` query feeding via `TyCtxt`

Instead of having a magic function that violates some `TyCtxtFeed` invariants, add a `create_def` equivalent for `CrateNum`s.

Note that this still isn't tracked by the query system (unlike `create_def`), and that feeding most `CrateNum` queries for crates other than the local one will likely cause performance regressions.

These things should be attempted on their own separately, but this PR should stand on its own

Author: bors