effects/overview: Make geometry updates handling more robust
The ExpoLayout delays relayouting for optimization purposes. However, this means that new geometry will be available only after returning to the event loop.
This change delays starting the intro animation so it can be started with new geometries.
Once an animation starts due to property change, it cannot be easily re-targeted. This can cause undesired animation jumps if a property changes during startup (for example from 0 to its final value).
With this change, the window heap's animation will be disabled until the effect starts the intro animation.
Edited by Vlad Zahorodnii