Stabilize Result::into_{ok,err}

[theemathas]

Tracking issue: #61695

---

As evidence of the demand of this API, here are some instances of people having written functions for this functionality:

• https://github.com/meteroid-oss/meteroid/blob/6cc14c4a444c6ae4889c603f5cb275ea626d7507/crates/common-utils/src/misc.rs#L7
• https://github.com/mokeyish/smartdns-rs/blob/788e83fa72477ebcf1c6a7f4482359353d29c480/src/server/http.rs#L93
• https://github.com/nostrdevkit/nostr/blob/ea38c0e3b2fc2717a4a55d019560a5574baf8cd0/nostr/src/util/mod.rs#L120
• https://github.com/ngrok/ngrok-rust/blob/3d5131559948ba9932dd0a450474fd1d19d206eb/ngrok/examples/tls.rs#L92
• https://github.com/octopii-rs/octopii/blob/b54c112d7db7ed1195dd4f600b4b786df85c8e7e/openraft/openraft/src/error/into_ok.rs#L10
• https://github.com/TeXitoi/keyseebee/blob/30956f62e618ed754c15af66f8ade70269fef89a/firmware/src/main.rs#L54

---

API being stabilized:

impl<T, E> Result<T, E> {
    pub fn into_ok(self) -> T
    where
        E: Into<!>
    { .... }
    pub fn into_err(self) -> E
    where
        T: Into<!>,
    { .... }
}

---

Implementation history: (I'm including only ones that touches the public API being stabilized, and not documentation or constification)

• RFC: Add method Result::into_ok rfcs#2799
• Add method Result::into_ok #66045
• Add Result::into_err where the Ok variant is the never type #83421
• Consolidate Result's and Option's methods into fewer impl blocks #92444

[rustbot]

clippy is developed in its own repository. If possible, consider making this change to rust-lang/rust-clippy instead.

cc @rust-lang/clippy

[rustbot]

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[nia-e]

@rfcbot fcp merge libs

[rust-rfcbot]

@nia-e has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
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• @joshtriplett
• @the8472
• @thomcc

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[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

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