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