layout: Place absolutes in IFCs at their hypothetical static position (#31418)

Absolutes need to be placed at their hypothetical position as if the
position value was static. This position differs based on the value they
had before blockification. The code for placing absolutes was taking
into account the original display for the inline value, but not for the
block value. A static `display: block` box would placed at a new block
position past the end of the linebox.

components/layout_2020/dom_traversal.rs

@@ -89,6 +89,7 @@ where
     }
 }
 
+#[derive(Debug)]
 pub(super) enum Contents {
     /// Refers to a DOM subtree, plus `::before` and `::after` pseudo-elements.
     OfElement,
@@ -107,6 +108,7 @@ pub(super) enum NonReplacedContents {
     OfPseudoElement(Vec<PseudoElementContentItem>),
 }
 
+#[derive(Debug)]
 pub(super) enum PseudoElementContentItem {
     Text(String),
     Replaced(ReplacedContent),