[ios] Renamed custom style layer invalidation method

Cf. -[UIView setNeedsDisplay] and -[MKOverlayRenderer setNeedsDisplay].

include/mbgl/ios/MGLMapView+MGLCustomStyleLayerAdditions.h

@@ -20,7 +20,7 @@ typedef void (^MGLCustomStyleLayerCompletionHandler)(void);
 
 - (void)insertCustomStyleLayerWithIdentifier:(NSString *)identifier preparationHandler:(MGLCustomStyleLayerPreparationHandler)preparation drawingHandler:(MGLCustomStyleLayerDrawingHandler)drawing completionHandler:(MGLCustomStyleLayerCompletionHandler)completion belowStyleLayerWithIdentifier:(nullable NSString *)otherIdentifier;
 
-- (void)invalidateCustomStyleLayers;
+- (void)setCustomStyleLayersNeedDisplay;
 
 @end
 

platform/ios/MGLMapView.mm

@@ -3675,7 +3675,7 @@ void MGLFinishCustomStyleLayer(void *context)
                              context, otherIdentifier.UTF8String);
 }
 
-- (void)invalidateCustomStyleLayers
+- (void)setCustomStyleLayersNeedDisplay
 {
     _mbglMap->update(mbgl::Update::Repaint);
 }