Support shape annotations on GLFWView

Add different random triangles count by using the keys 7, 8, 9 or 0.
Q will clear all the annotations.
W will remove one annotation.

include/mbgl/platform/default/glfw_view.hpp

@@ -37,7 +37,15 @@ public:
     void fps();
 
 private:
+    mbgl::LatLng makeRandomPoint() const;
+
     void addRandomPointAnnotations(int count);
+    void addRandomShapeAnnotations(int count);
+
+    void clearAnnotations();
+    void popAnnotation();
+
+    mbgl::AnnotationIDs annotationIDs;
 
 private:
     bool fullscreen = false;