Rollup merge of #87175 - inquisitivecrystal:inner-error, r=kennytm
Rollup merge of #87175 - inquisitivecrystal:inner-error, r=kennytm

Stabilize `into_parts()` and `into_error()`

This stabilizes `IntoInnerError`'s `into_parts()` and `into_error()` methods, currently gated behind the `io_into_inner_error_parts` feature. The FCP has [already completed.](https://github.com/rust-lang/rust/issues/79704#issuecomment-880652967)

Closes #79704.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust