Make use of NoHash hashing for FileId and CrateId
Both of these are mere integers so there is nothing to hash here.
Ideally we would use this for `la_arena::Idx` too, but that doesn't work due to the orphan rule, and `la_arena` is unfortunately a public library so we can't really do much here... Unless we remove the trait restriction but I'd like not to
ca8093e282