add Iterator::dedup and friends

[Qelxiros]

Tracking issue: #83747

[rustbot]

r? @ibraheemdev

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[rustbot]

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[ibraheemdev]

r? libs-api

[rust-log-analyzer]

The job pr-check-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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

[RUSTC-TIMING] askama test:false 0.520
error: a method with this name may be added to the standard library in the future
   --> src/tools/clippy/clippy_lints/src/macro_metavars_in_unsafe.rs:275:14
    |
275 |             .dedup_by(|&(_, a), &(_, b)| a == b);
    |              ^^^^^^^^
    |
    = warning: once this associated item is added to the standard library, the ambiguity may cause an error or change in behavior!
    = note: for more information, see issue #48919 <https://github.com/rust-lang/rust/issues/48919>
    = help: call with fully qualified syntax `itertools::Itertools::dedup_by(...)` to keep using the current method
    = note: `-D unstable-name-collisions` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unstable_name_collisions)]`
help: add `#![feature(iter_dedup)]` to the crate attributes to enable `std::iter::Iterator::dedup_by`
   --> src/tools/clippy/clippy_lints/src/lib.rs:33:1
    |
 33 + #![feature(iter_dedup)]
    |

[RUSTC-TIMING] clippy_lints test:false 19.165
error: could not compile `clippy_lints` (lib) due to 1 previous error
Bootstrap failed while executing `check --target=i686-pc-windows-gnu --host=i686-pc-windows-gnu`

[dtolnay]

Thanks for the PR!

I expect that this is going to be blocked on compiler work (#89151) for the same reason as this other pending Iterator method: #141994.

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