Point out the type of associated types in every method call of iterator chains

[estebank]

Partially address #105184 by pointing out the type of associated types in every method call of iterator chains:

note: the expression is of type `Map<std::slice::Iter<'_, {integer}>, [closure@src/test/ui/iterators/invalid-iterator-chain.rs:12:18: 12:21]>`
    --> src/test/ui/iterators/invalid-iterator-chain.rs:12:14
     |
10   |         vec![0, 1]
     |         ---------- this expression has type `Vec<{integer}>`
11   |             .iter()
     |              ------ associated type `std::iter::Iterator::Item` is `&{integer}` here
12   |             .map(|x| { x; })
     |              ^^^^^^^^^^^^^^^ associated type `std::iter::Iterator::Item` is `()` here

We also reduce the number of impls we mention when any of the candidates is an "exact match". This benefits the output of cases with numerics greatly.

Outstanding work would be to provide a structured suggestion for appropriate changes, like in this case detecting the spurious ; in the closure.

[rustbot]

r? @lcnr

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[compiler-errors]

I think 42847b08439f853116064ec37c255db4776a5e2d should be pulled into a different PR since it's unrelated.

[oli-obk]

r? @oli-obk

[oli-obk]

Could be a good opportunity to move the entire ObligationCauseCode::FunctionArgumentObligation arm into a new module

[oli-obk]

@bors r+

[bors]

📌 Commit f4ed2d1 has been approved by oli-obk

It is now in the queue for this repository.