Allow to update depending rect calculations at the same time

[garthenweb]

When deferUpdateUntilIdle or priority: 'high' | 'normal' | 'low'' } is used for multiple items and the updates result in the same calculation, the updates will happen once after another. Dependent of the order, which is not predictable in every case, it can even result in different results.

The goal would be to find an API that allows to observe multiple elements and get one update for all of them at once.