Rollup merge of #82917 - cuviper:iter-zip, r=m-ou-se

Add function core::iter::zip

This makes it a little easier to `zip` iterators:

```rust
for (x, y) in zip(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().zip(ys) {}
```

You can `zip(&mut xs, &ys)` for the conventional `iter_mut()` and
`iter()`, respectively. This can also support arbitrary nesting, where
it's easier to see the item layout than with arbitrary `zip` chains:

```rust
for ((x, y), z) in zip(zip(xs, ys), zs) {}
for (x, (y, z)) in zip(xs, zip(ys, zs)) {}
// vs.
for ((x, y), z) in xs.into_iter().zip(ys).zip(xz) {}
for (x, (y, z)) in xs.into_iter().zip((ys.into_iter().zip(xz)) {}
```

It may also format more nicely, especially when the first iterator is a
longer chain of methods -- for example:

```rust
    iter::zip(
        trait_ref.substs.types().skip(1),
        impl_trait_ref.substs.types().skip(1),
    )
    // vs.
    trait_ref
        .substs
        .types()
        .skip(1)
        .zip(impl_trait_ref.substs.types().skip(1))
```

This replaces the tuple-pair `IntoIterator` in #78204.
There is prior art for the utility of this in [`itertools::zip`].

[`itertools::zip`]: https://docs.rs/itertools/0.10.0/itertools/fn.zip.html

library/std/src/lib.rs

@@ -278,6 +278,7 @@
 #![feature(integer_atomics)]
 #![feature(into_future)]
 #![feature(intra_doc_pointers)]
+#![feature(iter_zip)]
 #![feature(lang_items)]
 #![feature(link_args)]
 #![feature(linkage)]

library/std/src/sys/unix/ext/net/addr.rs

@@ -2,7 +2,7 @@ use crate::ffi::OsStr;
 use crate::os::unix::ffi::OsStrExt;
 use crate::path::Path;
 use crate::sys::cvt;
-use crate::{ascii, fmt, io, mem};
+use crate::{ascii, fmt, io, iter, mem};
 
 // FIXME(#43348): Make libc adapt #[doc(cfg(...))] so we don't need these fake definitions here?
 #[cfg(not(unix))]
@@ -41,7 +41,7 @@ pub(super) unsafe fn sockaddr_un(path: &Path) -> io::Result<(libc::sockaddr_un,
             &"path must be shorter than SUN_LEN",
         ));
     }
-    for (dst, src) in addr.sun_path.iter_mut().zip(bytes.iter()) {
+    for (dst, src) in iter::zip(&mut addr.sun_path, bytes) {
         *dst = *src as libc::c_char;
     }
     // null byte for pathname addresses is already there because we zeroed the