Create gray -> grey doc aliases (#5362)

As someone who uses "grey" instead of "gray", it is annoying that my
autocomplete can never find any of the "gray" color related things, so
this adds doc aliases for that.

* [x] I have followed the instructions in the PR template

crates/epaint/src/image.rs

@@ -124,6 +124,7 @@ impl ColorImage {
     /// Create a [`ColorImage`] from iterator over flat opaque gray data.
     ///
     /// Panics if `size[0] * size[1] != gray_iter.len()`.
+    #[doc(alias = "from_grey_iter")]
     pub fn from_gray_iter(size: [usize; 2], gray_iter: impl Iterator<Item = u8>) -> Self {
         let pixels: Vec<_> = gray_iter.map(Color32::from_gray).collect();
         assert_eq!(size[0] * size[1], pixels.len());