fix(loading): include cssClass in the Loading options

added to test as well

fixes #6365

ionic/components/loading/loading.ts

@@ -224,6 +224,7 @@ class LoadingCmp {
 export interface LoadingOptions {
   spinner?: string;
   content?: string;
+  cssClass?: string;
   showBackdrop?: boolean;
   dismissOnPageChange?: boolean;
   delay?: number;

ionic/components/loading/test/basic/index.ts

@@ -10,7 +10,8 @@ class E2EPage {
   presentLoadingIos() {
     let loading = Loading.create({
       spinner: 'ios',
-      duration: 1000
+      duration: 1000,
+      cssClass: 'my-custom-loader'
     });
 
     loading.onDismiss(() => {