macos support for polyline/polygon coordinates mutation

platform/macos/src/MGLMapView.mm

@@ -482,6 +482,25 @@ - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(_
                 [self deselectAnnotation:annotation];
             }
         }
+    } else if ([keyPath isEqualToString:@"coordinates"] &&
+               [object isKindOfClass:[MGLMultiPoint class]]) {
+        MGLMultiPoint *annotation = object;
+        MGLAnnotationTag annotationTag = (MGLAnnotationTag)(NSUInteger)context;
+        // We can get here because a subclass registered itself as an observer
+        // of the coordinates key path of a multipoint annotation but failed
+        // to handle the change. This check deters us from treating the
+        // subclass’s context as an annotation tag. If the context happens to
+        // match a valid annotation tag, the annotation will be unnecessarily
+        // but safely updated.
+        if (annotation == [self annotationWithTag:annotationTag]) {
+            _mbglMap->updateAnnotation(annotationTag, [annotation annotationObjectWithDelegate:self]);
+            // We don't current support shape multipoint annotation selection, but let's make sure
+            // deselection is handled just to avoid problems in the future.
+            if (annotationTag == _selectedAnnotationTag)
+            {
+                [self deselectAnnotation:annotation];
+            }
+        }
     }
 }
 
@@ -1625,6 +1644,8 @@ - (void)addAnnotations:(NS_ARRAY_OF(id <MGLAnnotation>) *)annotations {
             MGLAnnotationContext context;
             context.annotation = annotation;
             _annotationContextsByAnnotationTag[annotationTag] = context;
+
+            [(NSObject *)annotation addObserver:self forKeyPath:@"coordinates" options:0 context:(void *)(NSUInteger)annotationTag];
         } else if (![annotation isKindOfClass:[MGLMultiPolyline class]]
                    || ![annotation isKindOfClass:[MGLMultiPolygon class]]
                    || ![annotation isKindOfClass:[MGLShapeCollection class]]) {
@@ -1762,6 +1783,8 @@ - (void)removeAnnotations:(NS_ARRAY_OF(id <MGLAnnotation>) *)annotations {
         if ([annotation isKindOfClass:[NSObject class]] &&
             ![annotation isKindOfClass:[MGLMultiPoint class]]) {
             [(NSObject *)annotation removeObserver:self forKeyPath:@"coordinate" context:(void *)(NSUInteger)annotationTag];
+        } else if ([annotation isKindOfClass:[MGLMultiPoint class]]) {
+            [(NSObject *)annotation removeObserver:self forKeyPath:@"coordinates" context:(void *)(NSUInteger)annotationTag];
         }
 
         _mbglMap->removeAnnotation(annotationTag);