Implement MGLForegroundStyleLayer.sourceIdentifier (#7570)

* [ios, macos] sourceIdentifier accessor methods

* [ios, macos] generate style code

platform/darwin/src/MGLCircleStyleLayer.mm

@@ -54,6 +54,13 @@ namespace mbgl {
     super.rawLayer = rawLayer;
 }
 
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
 - (NSString *)sourceLayerIdentifier
 {
     MGLAssertStyleLayerIsValid();

platform/darwin/src/MGLFillStyleLayer.mm

@@ -49,6 +49,13 @@ namespace mbgl {
     super.rawLayer = rawLayer;
 }
 
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
 - (NSString *)sourceLayerIdentifier
 {
     MGLAssertStyleLayerIsValid();

platform/darwin/src/MGLLineStyleLayer.mm

@@ -61,6 +61,13 @@ namespace mbgl {
     super.rawLayer = rawLayer;
 }
 
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
 - (NSString *)sourceLayerIdentifier
 {
     MGLAssertStyleLayerIsValid();

platform/darwin/src/MGLRasterStyleLayer.mm

@@ -41,6 +41,13 @@
     super.rawLayer = rawLayer;
 }
 
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
 #pragma mark - Adding to and removing from a map view
 
 - (void)addToMapView:(MGLMapView *)mapView belowLayer:(MGLStyleLayer *)otherLayer

platform/darwin/src/MGLStyleLayer.mm.ejs

@@ -89,7 +89,15 @@ namespace mbgl {
     super.rawLayer = rawLayer;
 }
 
-<% if (type !== 'background' && type !== 'raster') { -%>
+<% if (type !== 'background') { -%>
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
+<% if (type !== 'raster') { -%>
 - (NSString *)sourceLayerIdentifier
 {
     MGLAssertStyleLayerIsValid();
@@ -119,7 +127,7 @@ namespace mbgl {
     return [NSPredicate mgl_predicateWithFilter:self.rawLayer->getFilter()];
 }
 
-<% } -%>
+<% }} -%>
 #pragma mark - Adding to and removing from a map view
 
 - (void)addToMapView:(MGLMapView *)mapView belowLayer:(MGLStyleLayer *)otherLayer

platform/darwin/src/MGLSymbolStyleLayer.mm

@@ -108,6 +108,13 @@ namespace mbgl {
     super.rawLayer = rawLayer;
 }
 
+- (NSString *)sourceIdentifier
+{
+    MGLAssertStyleLayerIsValid();
+    
+    return @(self.rawLayer->getSourceID().c_str());
+}
+
 - (NSString *)sourceLayerIdentifier
 {
     MGLAssertStyleLayerIsValid();