Support IE Indeterminate checkboxes for "All" option

IE handles indeterminate checkboxes "differently", it doesn't fire an
onChange event when a checkbox goes from indeterminate to a determinate
state.

This issue is well documented on the jquery github issue:
jquery/jquery#1698

The generally accepted solution is to use the onClick event instead of the
onChange event. You can see this solution implemented in the google's angular
material design library in their github link here:

angular/components#3145

I applied a similar approach to normalize the events we listen to for the
indeterminate all checkbox and commented why those things are done in the
code so this issue won't regress.

Author: Daniel Latimer

src/lib/treeview.component.html

@@ -23,8 +23,7 @@
     <div *ngIf="config.hasAllCheckBox || config.hasCollapseExpand" class="row row-all">
       <div class="col-12">
         <div class="form-check">
-          <input type="checkbox" class="form-check-input" [(ngModel)]="item.checked" (ngModelChange)="onCheckedChange()" [indeterminate]="item.indeterminate"
-          />
+          <input type="checkbox" class="form-check-input" [(ngModel)]="item.checked" [indeterminate]="item.indeterminate" (click)="onCheckedChange()"/>
           <label *ngIf="config.hasAllCheckBox" class="form-check-label" (click)="item.checked = !item.checked; onCheckedChange()">
             {{i18n.getAllCheckboxText()}}
           </label>

src/lib/treeview.component.ts

@@ -100,16 +100,34 @@ export class TreeviewComponent implements OnChanges {
         this.updateFilterItems();
     }
 
+    /**
+     * IE has an issue where it does not send a change event for when an indeterminate checkbox changes to become determinate.
+     * To work around this we explicity set it checked if it's indeterminate and we use the onClick event instead of onChange.
+     */
     onAllCheckedChange() {
-        const checked = this.allItem.checked;
-        this.filterItems.forEach(item => {
-            item.setCheckedRecursive(checked);
-            if (item instanceof FilterTreeviewItem) {
-                item.updateRefChecked();
+        this.standardizeEventOrder(() => {
+            if (this.allItem.indeterminate) {
+                this.allItem.checked = true;
             }
-        });
 
-        this.raiseSelectedChange();
+            const checked = this.allItem.checked;
+            this.filterItems.forEach(item => {
+                item.setCheckedRecursive(checked);
+                if (item instanceof FilterTreeviewItem) {
+                    item.updateRefChecked();
+                }
+            });
+
+            this.raiseSelectedChange();
+        })
+    }
+
+    /**
+     * IE performs the onClick event before the onChange event while Chrome and perform it in the other order.
+     * By pushing the callback onto the event queue it will always be executed immediately after all pending events
+     */
+    standardizeEventOrder(callback) {
+      setTimeout(callback, 0);
     }
 
     onItemCheckedChange(item: TreeviewItem, checked: boolean) {