Finish documenting the action, asset, color, and element modules in GPUI

Remove SmallVec from the public API of GPUI

crates/ui/src/components/label/label_like.rs

@@ -78,8 +78,8 @@ impl LabelCommon for LabelLike {
 }
 
 impl ParentElement for LabelLike {
-    fn children_mut(&mut self) -> &mut SmallVec<[AnyElement; 2]> {
-        &mut self.children
+    fn extend(&mut self, elements: impl Iterator<Item = AnyElement>) {
+        self.children.extend(elements)
     }
 }