layout: Add a first pass at incremental box tree construction (#37751)

This change:

- Adds a new type of LayoutDamage that signifies that a box needs its
  children recollected, because one or more of them need to be rebuilt.
- During restyle damage propagation, propagate this new damage upward in
  the tree. Then box tree construction should be able to preserve any
  still-valid box tree nodes from box slots.
- During BlockLevelBox job finalization, if a box slot is valid and
  there is not LayoutDamage to the element, use the old box slot,
  ensuring that its fragment cache is invalidated.

Testing: This should not change observable behavior and thus is covered
by existing WPT tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: coding-joedow <ibluegalaxy_taoj@163.com>

components/script/dom/document.rs

@@ -936,7 +936,7 @@ impl Document {
 
         // FIXME(emilio): This is very inefficient, ideally the flag above would
         // be enough and incremental layout could figure out from there.
-        node.dirty(NodeDamage::Other);
+        node.dirty(NodeDamage::ContentOrHeritage);
     }
 
     /// Remove any existing association between the provided id and any elements in this document.