rustdoc doesn't detect + warn about broken anchor links, unlike regular intra-doc links

[dj8yfo]

Not sure what category this should be. This one is much more of a feature request, than a bug.

The term of what is meant by anchors is borrowed from here #62833 .

cargo-deadlinks https://github.com/deadlinks/cargo-deadlinks does detect these, but is somewhat unofficial and is not as convenient to use as the rustdoc / cargo doc .