Add copy button to crate version.

[MeetThePatel]

This PR closes #111143.

Instead of copying strictly the crate version number, this implementation copies a Cargo.toml 'snippet' (the same behavior as the Crates.io copy button). i.e. For a crate called very_useful_crate on version 0.1.0, the copied string would be: very_useful_crate = "0.1.0".

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @GuillaumeGomez (or someone else) some time within the next two weeks.

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[rustbot]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

.......... (130/131)
F          (131/131)


/checkout/tests/rustdoc-gui/sidebar.goml sidebar... FAILED
[ERROR] `tests/rustdoc-gui/sidebar.goml` line 200: The following errors happened: [different X values: -5.453125 (or -5) != -3]: for command `assert-position: (".sidebar-crate > h2 > a", {"x": -3})`
Error: ()
Build completed unsuccessfully in 0:03:18
  local time: Sat Sep 14 23:53:36 UTC 2024
  network time: Sat, 14 Sep 2024 23:53:37 GMT