Reverse after flattening when iterating paint_children for hit_testing.

The flatten step flattens an Option<Vec<T>>, so if we reverse before
flattening then we are only reversing the order of iteration over the
Option (which has no effect).

packages/blitz-dom/src/node.rs

@@ -1001,8 +1001,8 @@ impl Node {
         self.paint_children
             .borrow()
             .iter()
-            .rev()
             .flatten()
+            .rev()
             .find_map(|&i| self.with(i).hit(x, y))
             .or(Some(HitResult {
                 node_id: self.id,