[ios] Ensure mapView is set when positioning (#5647)

Ensure the mapView property is set when positioning the annotation view, in case the map view needs to be consulted about its rotation or pitch.

platform/ios/src/MGLMapView.mm

@@ -4586,8 +4586,8 @@ mbgl::Duration MGLDurationInSeconds(NSTimeInterval duration)
                     [self.glView addSubview:annotationView];
                 }
                 
-                annotationView.center = [self convertCoordinate:annotationContext.annotation.coordinate toPointToView:self];
                 annotationView.mapView = self;
+                annotationView.center = [self convertCoordinate:annotationContext.annotation.coordinate toPointToView:self];
                 annotationContext.annotationView = annotationView;
             }
         }