refactor(pull-to-refresh): rename the starting event to start

updated docs to reflect new name and renamed an internal function

BREAKING CHANGE: starting event no longer exists, must use start

References #5207

ionic/components/scroll/test/pull-to-refresh/index.ts

@@ -14,7 +14,7 @@ class E2EApp {
   }
 
   doRefresh(refresher) {
-    console.log('Refreshing', refresher)
+    console.log('Doing Refresh', refresher)
 
     // Add to the top of the list on refresh
     let firstIndex = this.items[0].index - 1;
@@ -29,8 +29,8 @@ class E2EApp {
     }, 5000);
   }
 
-  doStarting(refresher) {
-    console.log('Starting', refresher);
+  doStart(refresher) {
+    console.log('Doing Start', refresher);
   }
 
   doPulling(refresher) {

ionic/components/scroll/test/pull-to-refresh/main.html

@@ -2,7 +2,7 @@
 
 <ion-content>
   <ion-refresher
-    (starting)="doStarting($event)"
+    (start)="doStart($event)"
     (refresh)="doRefresh($event)"
     (pulling)="doPulling($event)"
     pullingIcon="heart"