Add missing sourceDidChange event (#3421)

platform/macos/src/MLNMapView.mm

@@ -984,6 +984,11 @@ public:
     if (!_mbglMap) {
         return;
     }
+
+    if ([self.delegate respondsToSelector:@selector(mapView:sourceDidChange:)]) {
+        [self.delegate mapView:self sourceDidChange:source];
+    }
+
     // Attribution only applies to tiled sources
     if ([source isKindOfClass:[MLNTileSource class]]) {
         [self installAttributionView];

platform/macos/src/MLNMapViewDelegate.h

@@ -204,6 +204,14 @@ NS_ASSUME_NONNULL_BEGIN
  */
 - (void)mapView:(MLNMapView *)mapView didFinishLoadingStyle:(MLNStyle *)style;
 
+/**
+ Tells the delegate that the source changed.
+
+ @param mapView The map view that owns the source.
+ @param source The source that changed.
+ */
+- (void)mapView:(MLNMapView *)mapView sourceDidChange:(MLNSource *)source;
+
 /**
  Tells the delegate that the `mapView` is missing an image. The image should be added synchronously
  with ``MLNStyle/setImage:forName:`` to be rendered on the current zoom level. When loading icons

platform/macos/test/MLNMapViewDelegateIntegrationTests.swift

@@ -38,6 +38,8 @@ extension MLNMapViewDelegateIntegrationTests: MLNMapViewDelegate {
 
     func mapView(_: MLNMapView, didFinishLoading _: MLNStyle) {}
 
+    func mapView(_: MLNMapView, sourceDidChange _: MLNSource) {}
+
     func mapViewWillStartRenderingFrame(_: MLNMapView) {}
 
     func mapViewWillStartRenderingMap(_: MLNMapView) {}