layout: Simplify and generalize the usage of pseudo-elements (#36202)

- Remove the last remaining Servo-specific PseudoElement enum from
  layout. This was made to select `::before` and `::after` (both eager
  pseudo-elements), but now `traverse_pseudo_element` is called
  `traverse_eager_pseudo_element` and should work on any eager pseudo
  element.
- Expose a single way of getting psuedo-element variants of
  ThreadSafeLayoutElement in the Layout DOM, which returns `None` when
  the pseudo-element doesn't apply (not defined for eager
  pseudo-elements or when trying to get `<details>` related
  pseudo-elements on elements that they don't apply to).
- Ensure that NodeAndStyleInfo always refers to a node. This is done by
  making sure that anonymous boxes are all associated with their
  originating node.

These changes are prepatory work for implementation of the `::marker`
pseudo-element as well as ensuring that all anonymous boxes can be
cached into the box tree eventually.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/script/layout_dom/element.rs

@@ -14,6 +14,7 @@ use script_layout_interface::wrapper_traits::{
     LayoutNode, ThreadSafeLayoutElement, ThreadSafeLayoutNode,
 };
 use script_layout_interface::{LayoutNodeType, StyleData};
+use selectors::Element as _;
 use selectors::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
 use selectors::bloom::{BLOOM_HASH_MASK, BloomFilter};
 use selectors::matching::{ElementSelectorFlags, MatchingContext, VisitedHandlingMode};
@@ -805,11 +806,35 @@ impl<'dom> ThreadSafeLayoutElement<'dom> for ServoThreadSafeLayoutElement<'dom>
         self.pseudo
     }
 
-    fn with_pseudo(&self, pseudo: PseudoElement) -> Self {
-        ServoThreadSafeLayoutElement {
-            element: self.element,
-            pseudo: Some(pseudo),
+    fn with_pseudo(&self, pseudo_element_type: PseudoElement) -> Option<Self> {
+        if pseudo_element_type.is_eager() &&
+            self.style_data()
+                .styles
+                .pseudos
+                .get(&pseudo_element_type)
+                .is_none()
+        {
+            return None;
         }
+
+        if pseudo_element_type == PseudoElement::DetailsSummary &&
+            (!self.has_local_name(&local_name!("details")) || !self.has_namespace(&ns!(html)))
+        {
+            return None;
+        }
+
+        if pseudo_element_type == PseudoElement::DetailsContent &&
+            (!self.has_local_name(&local_name!("details")) ||
+                !self.has_namespace(&ns!(html)) ||
+                self.get_attr(&ns!(), &local_name!("open")).is_none())
+        {
+            return None;
+        }
+
+        Some(ServoThreadSafeLayoutElement {
+            element: self.element,
+            pseudo: Some(pseudo_element_type),
+        })
     }
 
     fn type_id(&self) -> Option<LayoutNodeType> {