chore(switch): ios impl of onBackgroundColor

Author: farfromrefug

src/switch/index.ios.ts

@@ -1,4 +1,14 @@
-import { SwitchBase } from './index-common';
+import { SwitchBase, onBackgroundColorProperty } from './index-common';
 
 // TODO: for now iOS uses system switch
-export class Switch extends SwitchBase {}
+export class Switch extends SwitchBase {
+
+  [onBackgroundColorProperty.setNative](value) {
+        if (value) {
+            this.nativeViewProtected.onTintColor = value instanceof Color ? value.ios : value;
+        }
+        else {
+            this.nativeViewProtected.onTintColor = null;
+        }
+    }
+}