[ios, macos] Use swift_name for MGLMultiPoint and subclasses (#6727)

Decorate the class factory methods so that when they are translated to
swift the method to create an MGLMultiPoint is not ambiguous with the
methods to create MGLPolygon and MGLPolyline.

platform/darwin/src/MGLMultiPoint.h

@@ -22,7 +22,7 @@ NS_ASSUME_NONNULL_BEGIN
  @param count The number of items in the `coords` array.
  @return A new multipoint object.
  */
-+ (instancetype)multiPointWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count;
++ (instancetype)multiPointWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count NS_SWIFT_NAME(multiPoint(coordinates:count:));
 
 /**
  The array of coordinates associated with the shape.

platform/darwin/src/MGLPolygon.h

@@ -36,7 +36,7 @@ NS_ASSUME_NONNULL_BEGIN
  @param count The number of items in the `coords` array.
  @return A new polygon object.
  */
-+ (instancetype)polygonWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count;
++ (instancetype)polygonWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count NS_SWIFT_NAME(polygon(coordinates:count:));
 
 /**
  Creates and returns an `MGLPolygon` object from the specified set of

platform/darwin/src/MGLPolyline.h

@@ -25,8 +25,7 @@ NS_ASSUME_NONNULL_BEGIN
  @param count The number of items in the `coords` array.
  @return A new polyline object.
  */
-+ (instancetype)polylineWithCoordinates:(CLLocationCoordinate2D *)coords
-                                  count:(NSUInteger)count;
++ (instancetype)polylineWithCoordinates:(CLLocationCoordinate2D *)coords count:(NSUInteger)count NS_SWIFT_NAME(polyline(coordinates:count:));
 
 @end