LibWeb: Compute position of relative blocks before placing them

Turns out compute_position should be invoked before placing the element
in normal flow. Otherwise, the position isn't set on the first layout.
The effect was that the block would "jump" into place on a secondary
layout.

This is a follow-up to commit:
deda7c899525eeb989ab79d5d9e24d685569c84d

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -409,14 +409,14 @@ void BlockFormattingContext::layout_block_level_children(Box& box, LayoutMode la
         layout_inside(child_box, layout_mode);
         compute_height(child_box);
 
+        if (child_box.computed_values().position() == CSS::Position::Relative)
+            compute_position(child_box);
+
         if (is<ReplacedBox>(child_box))
             place_block_level_replaced_element_in_normal_flow(child_box, box);
         else if (is<BlockBox>(child_box))
             place_block_level_non_replaced_element_in_normal_flow(child_box, box);
 
-        if (child_box.computed_values().position() == CSS::Position::Relative)
-            compute_position(child_box); // Note: Shifting position should occur after the above layout.
-
         // FIXME: This should be factored differently. It's uncool that we mutate the tree *during* layout!
         //        Instead, we should generate the marker box during the tree build.
         if (is<ListItemBox>(child_box))