Implementation: #7903
Original issue: #1681

Summary

-Z crate-versions will add the crate version to cargo doc via the unstable rustdoc flag.

Unresolved issues

• Need to stabilize --crate-version in rustdoc. DONE: Stabilize --crate-version option in rustdoc rust#69494
• Wait for --crate-version to hit stable (1.44 on June 4th). (This is done so we don't have to query rustdoc if it supports the flag.)