A mode to simply sync versions in Cargo.toml to Cargo.lock

[AMDmi3]

There could be a dead simple mode of operation which just syncs versions in Cargo.toml(s) to ones from the lock file. This would allow cargo upgrade to be usable/compatible with other tools which on operate on lockfiles, such as new cargo min-publish-age setting.

[epage]

Overall, our aim for cargo uprade at this point is to explore what should an upstream cargo command look like. I see this kind of sync to be less likely to fit within that scheme.

However, I have proposed such a lint for cargo rust-lang/cargo#15583 which would eventually be fixable with cargo fix