Dashboard: fix view panel mode for Safari / iOS (#28702)

* fix(dashboard): flex-basis so child height percentages are respected

* fix(dashboard): reset scrollTop when entering view panel mode

public/app/features/dashboard/containers/DashboardPage.tsx

@@ -145,6 +145,7 @@ export class DashboardPage extends PureComponent<Props, State> {
         this.setState({
           viewPanel: panel,
           rememberScrollTop: this.state.scrollTop,
+          updateScrollTop: 0,
         });
       });
     }

public/sass/pages/_dashboard.scss

@@ -18,6 +18,7 @@
 
 .dashboard-content {
   padding: $dashboard-padding;
+  flex-basis: 100%;
   flex-grow: 1;
 }