Add `ol.ObjectEvent` for changes to `ol.Object` properties. Previously, `ol.Object` dispatched instances of `goog.events.Event` with type `change`. Now `ol.ObjectEvent` instances will be dispatched on property changes. The events include a `getKey` method to get the name of the property being changed. The `beforepropertychange` type event is fired before a property value changes, and the `propertychange` type event fires after the property value changes.
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