Fix stale layout when a child switches to display: contents after insertion

Summary:
Each node caches how many of its children use `display: contents` (`contentsChildrenCount_`, added in react/yoga#1726). The count is updated in `insertChild`, `removeChild`, `replaceChild` and `setChildren`, but not when the display of a child that is already attached changes.

So if `YGNodeStyleSetDisplay(child, YGDisplayContents)` is called after the child was inserted, the owner still reports `hasContentsChildren() == false`. The layout algorithm then skips `cleanupContentsNodesRecursively` for it, and the contents node keeps `isDirty == true` after layout. When a descendant of that node changes later, `markDirtyAndPropagate` stops at the contents node because it is already dirty, the root is never marked dirty, and the next `YGNodeCalculateLayout` returns the cached layout.

Minimal repro:

```cpp
YGNodeRef root = YGNodeNew();
YGNodeStyleSetWidth(root, 100);
YGNodeStyleSetHeight(root, 100);
YGNodeRef child = YGNodeNew();
YGNodeInsertChild(root, child, 0);
YGNodeRef grandchild = YGNodeNew();
YGNodeStyleSetWidth(grandchild, 10);
YGNodeStyleSetHeight(grandchild, 10);
YGNodeInsertChild(child, grandchild, 0);

YGNodeStyleSetDisplay(child, YGDisplayContents);
YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);
// YGNodeIsDirty(child) is still true

YGNodeStyleSetWidth(grandchild, 20);
// YGNodeIsDirty(root) is false
YGNodeCalculateLayout(root, YGUndefined, YGUndefined, YGDirectionLTR);
// YGNodeLayoutGetWidth(grandchild) is 10, expected 20
```

This affects any binding that mutates nodes in place (the JS and Java bindings both go through `YGNodeStyleSetDisplay`). Setting the display before inserting the child works, which is what the existing tests do.

The fix recomputes the owner's count in `YGNodeStyleSetDisplay` when a node that has an owner switches to or from `display: contents`.

Changelog: [General][Fixed] - Fix stale layout when a child switches to `display: contents` after being inserted

X-link: react/yoga#2028

Reviewed By: javache

Differential Revision: D122122520

Pulled By: cipolleschi

Author: kwy404

packages/react-native/ReactCommon/yoga/yoga/YGNodeStyle.cpp

@@ -152,7 +152,16 @@ YGOverflow YGNodeStyleGetOverflow(const YGNodeConstRef node) {
 }
 
 void YGNodeStyleSetDisplay(const YGNodeRef node, const YGDisplay display) {
+  const bool wasContents =
+      resolveRef(node)->style().display() == Display::Contents;
   updateStyle<&Style::display, &Style::setDisplay>(node, scopedEnum(display));
+
+  // The owner caches how many of its children use display: contents, so it
+  // has to be recomputed when an attached child switches to or from it.
+  auto owner = resolveRef(node)->getOwner();
+  if (owner != nullptr && wasContents != (display == YGDisplayContents)) {
+    owner->setChildren(owner->getChildren());
+  }
 }
 
 YGDisplay YGNodeStyleGetDisplay(const YGNodeConstRef node) {