Change to use array::from_fn

Author: sorairolake

Diff for: library/core/src/array/mod.rs

@@ -430,12 +430,7 @@ impl<T: Clone, const N: usize> Clone for [T; N] {
 #[unstable(feature = "random", issue = "130703")]
 impl<T: Random, const N: usize> Random for [T; N] {
     fn random(source: &mut (impl RandomSource + ?Sized)) -> Self {
-        let mut buf = [const { MaybeUninit::uninit() }; N];
-        for elem in &mut buf {
-            elem.write(T::random(source));
-        }
-        // SAFETY: all elements of the array were initialized.
-        unsafe { mem::transmute_copy(&buf) }
+        from_fn(|_| T::random(source))
     }
 }