More fine grained dirty marking

Currently a node's dirty flag propagates to the root of the tree ensuring that when any node is invalidated its whole subtree will be re-calculated. This is often times not needed. There are many properties which only effects a node's children and would not need to propagate all the way to the root such as align-items. Also in cases where the style does change layout it may not need to propagate all the way to the root but can often stop at the nearest position: absolute parent.

This change has the potential of greatly improving performance of re-calculating a tree.

This might require adding a second dirty flag named hasDirtyChildren ensuring that traversal still works even though a parent is not marked as dirty.

Start by tracing how a node's dirty flag propagates during style invalidation, using the align-items example and the handling of position: absolute parents as boundaries. Determine how a separate hasDirtyChildren state would preserve traversal while limiting recalculation; done means localized invalidation remains correct and the tree recalculates less work.