Auto merge of #14745 - weihanglo:depinfo-compat, r=epage

docs(fingerprint): document the encoding of Cargo's depinfo

### What does this PR try to resolve?

When investigating #14712,
I figured that it lacks of docs for the Cargo's depinfo format.
Hence documenting them.

This PR also move dep info files related items to a separate module.

### How should we test and review this PR?

No behavior change, though I may submit a hack of #14712 after this.

I didn't move dep-info specific documentation into that new module.
It feels more nature for keeping them all in the fingerprint module.