Default implementation of CrateNum encoding/decoding should be disabled

[michaelwoerister]

The default implementation for CrateNum encoding and decoding should be disabled because the numeric value of a CrateNum can only be meaningfully interpreted giving the specific context of decoding (which the default decoder does not have access to). We already do something similar for DefIndex because it helps prevent bugs where decoding seems to work but really provides wrong values.

I already tried to make this change as part of #86368 (see 3eaeb92) but it turns out there's still one user of the default implementation related to -Zno-link.