[cesium] add constructor and removeProperty to PropertyBag (Definitel…

…yTyped#42803)

* [cesium] add constructor definition for PropertyBag

* Cesium - add removeProperty to PropertyBag

* Add return type to removeProperty

* Make constructor value optional

* Don't make parameters on callback optional

types/cesium/index.d.ts

@@ -121,11 +121,14 @@ declare namespace Cesium {
         readonly isConstant: boolean;
         propertyNames: string[];
 
-        addProperty(propertyName: string, value?: any, createPropertyCallback?: (value?: any) => void): void;
+        constructor(value?: object, createPropertyCallback?: (value?: any) => void);
+
+        addProperty(propertyName: string, value?: any, createPropertyCallback?: (value: any) => void): void;
         equals(other?: Property): boolean;
         getValue(time: JulianDate, result?: object): object;
         hasProperty(propertyName: string): boolean;
-        merge(source: object, createPropertyCallback?: (value?: any) => void): void;
+        merge(source: object, createPropertyCallback?: (value: any) => void): void;
+        removeProperty(propertyName: string): void;
     }
 
     class ArcGisImageServerTerrainProvider extends TerrainProvider {