rustdoc: Strikethrough deprecated items in sidebar

[Jules-Bertholet]

Fixes #107568 by indicating deprecated items in the sidebar with strikethrough.

This is my first Rustdoc contribution, and I would appreciate guidance on how to write/where to add tests.

@rustbot label A-rustdoc-ui T-rustdoc

[rustbot]

r? @GuillaumeGomez

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[rustbot]

Some changes occurred in src/librustdoc/clean/types.rs

cc @camelid

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @Folyd, @jsha

[GuillaumeGomez]

In this case, it would have been better to have wait for a decision to be reached because it's very likely that this solution will be either rejected or will be considered incomplete. And it's not great when contributors work for "nothing". :-/

I'm personally not a big fan of this approach but let's see what the rest of the team thinks about it.

cc @rust-lang/rustdoc

[bors]

☔ The latest upstream changes (presumably #114905) made this pull request unmergeable. Please resolve the merge conflicts.

[notriddle]

Consensus in the recent meeting seemed to reject this PR.

https://rust-lang.zulipchat.com/#narrow/stream/393423-t-rustdoc.2Fmeetings/topic/meeting.2004-09-2023/near/389048618

Thanks for the time, and sorry it didn't work out.