Compatibility with "cargo update --precise"

[Eh2406]

Implement compatibility with dtolnay/semver#321 . Check that the output make sense; it would be a shame for the new code also to have odd corner cases.

[Eh2406]

Here is a hack job to give it a try https://github.com/pubgrub-rs/semver-pubgrub/tree/new-pre-release

[Eh2406]

The upstream work moved to rust-lang/cargo#14305