Update Maps add-on documentation

[sukhova]

Describe Maps improvements 2.2:

• [x] Support Clustering in maps #2575
• [x] Zoom property type of GeoMapView and layers must be a double #2701
• [x] Provide Move and Zoom events #2719
• [ ] Add zoomTo methods to Map #2735
• [x] Support Heatmap layer in maps #2790
• [x] Provide injecting Layer and Source from Map to View controller #2799
• [x] Support MultiPoint, MultiPolygon, MultiLineString in Maps #2807
• [x] Provide utility classes for creating feature styles #2824