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/ecolor/src/rgba.rs

@@ -91,6 +91,7 @@ impl Rgba {
         Self([r, g, b, 1.0])
     }
 
+    #[doc(alias = "from_grey")]
     #[inline]
     pub const fn from_gray(l: f32) -> Self {
         Self([l, l, l, 1.0])