Auto merge of #79451 - usbalbin:array_zip, r=m-ou-se

Added [T; N]::zip()

This is my first PR to rust so I hope I have done everything right, or at least close :)

---

This is PR adds the array method `[T; N]::zip()` which, in my mind, is a natural extension to #75212.

My implementation of `zip()` is mostly just a modified copy-paste of `map()`. Should I keep the comments? Also am I right in assuming there should be no way for the `for`-loop to panic, thus no need for the dropguard seen in the `map()`-function?

The doc comment is in a similar way a slightly modified copy paste of [`Iterator::zip()`](https://doc.rust-lang.org/beta/std/iter/trait.Iterator.html#method.zip)

`@jplatte` mentioned in [#75490](https://github.com/rust-lang/rust/pull/75490#issuecomment-677790758) `zip_with()`,
> zip and zip_with seem like they would be useful :)

is this something I should add (assuming there is interest for this PR at all :))

library/core/src/array/mod.rs

@@ -463,6 +463,37 @@ impl<T, const N: usize> [T; N] {
         unsafe { crate::mem::transmute_copy::<_, [U; N]>(&dst) }
     }
 
+    /// 'Zips up' two arrays into a single array of pairs.
+    ///
+    /// `zip()` returns a new array where every element is a tuple where the
+    /// first element comes from the first array, and the second element comes
+    /// from the second array. In other words, it zips two arrays together,
+    /// into a single one.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_zip)]
+    /// let x = [1, 2, 3];
+    /// let y = [4, 5, 6];
+    /// let z = x.zip(y);
+    /// assert_eq!(z, [(1, 4), (2, 5), (3, 6)]);
+    /// ```
+    #[unstable(feature = "array_zip", issue = "80094")]
+    pub fn zip<U>(self, rhs: [U; N]) -> [(T, U); N] {
+        use crate::mem::MaybeUninit;
+
+        let mut dst = MaybeUninit::uninit_array::<N>();
+        for (i, (lhs, rhs)) in IntoIter::new(self).zip(IntoIter::new(rhs)).enumerate() {
+            dst[i].write((lhs, rhs));
+        }
+        // FIXME: Convert to crate::mem::transmute once it works with generics.
+        // unsafe { crate::mem::transmute::<[MaybeUninit<U>; N], [U; N]>(dst) }
+        // SAFETY: At this point we've properly initialized the whole array
+        // and we just need to cast it to the correct type.
+        unsafe { crate::mem::transmute_copy::<_, [(T, U); N]>(&dst) }
+    }
+
     /// Returns a slice containing the entire array. Equivalent to `&s[..]`.
     #[unstable(feature = "array_methods", issue = "76118")]
     pub fn as_slice(&self) -> &[T] {