layout: optimize the propagation and cleanup of RestyleDamage (#38199)

This change optimizes `RestyleDamage` propagation and cleanup to reduce
unnecessary box reconstruction and relayouts, while preventing damage
from the current reflow affecting subsequent ones. Improvements include:
- For box damage caused by `NodeDamage`, `RestyleDamage::RELAYOUT` is no
longer marked immediately—avoiding erroneous propagation of
`LayoutDamage::RECOLLECT_BOX_TREE_CHILDREN` to descendants during
`RestyleDamage` propagation.
- Clearing damage for nodes whose boxes will be preserved, preventing it
from carrying over to the next reflow and increasing its workload.

Testing: This should not change observable behavior and is thus covered
by existing WPT tests. Although Servo lacks performance test cases,
manual testing shows that this modification reduces reflow time by
nearly 250ms, representing a decrease of approximately 25%.

Signed-off-by: sharpshooter_pt <ibluegalaxy_taoj@163.com>

components/shared/layout/layout_damage.rs

@@ -21,12 +21,11 @@ bitflags! {
 
 impl LayoutDamage {
     pub fn recollect_box_tree_children() -> RestyleDamage {
-        RestyleDamage::from_bits_retain(LayoutDamage::RECOLLECT_BOX_TREE_CHILDREN.bits()) |
-            RestyleDamage::RELAYOUT
+        RestyleDamage::from_bits_retain(LayoutDamage::RECOLLECT_BOX_TREE_CHILDREN.bits())
     }
 
     pub fn rebuild_box_tree() -> RestyleDamage {
-        RestyleDamage::from_bits_retain(LayoutDamage::REBUILD_BOX.bits()) | RestyleDamage::RELAYOUT
+        RestyleDamage::from_bits_retain(LayoutDamage::REBUILD_BOX.bits())
     }
 
     pub fn has_box_damage(&self) -> bool {