[@types/cesium] Add PropertyBag (#42782)
[@types/cesium] Add PropertyBag (#42782)

* property Bag

* add entity definition

georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,dsebastien/DefinitelyTyped,markogresak/DefinitelyTyped,mcliment/DefinitelyTyped