fix(a11y): treeview incorrect levels (backport to 16.x) (#1385)

Backport 9c67c41 from #1383. <br> ## PR
Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)
- [ ] If applicable, have a visual design approval

## PR Type

What kind of change does this PR introduce?

&lt;!-- Please check the one that applies to this PR using
&quot;x&quot;. --&gt;

- [x] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, local variables)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Build related changes
- [ ] CI related changes
- [ ] Documentation content changes
- [ ] Other... Please describe:

## What is the current behavior?

&lt;!-- Please describe the current behavior that you are modifying, or
link to a relevant issue. --&gt;
The screen reader is reading out incorrect levels in case of a recursive
tree view component.
Issue Number: CDE-1697

## What is the new behavior?
The screen reader will read out correct levels for the recursive tree
view
## Does this PR introduce a breaking change?

- [ ] Yes
- [x] No

&lt;!-- If this PR contains a breaking change, please describe the
impact and migration path for existing applications below. --&gt;

## Other information

Co-authored-by: Andrea A Fernandes <[email protected]>

projects/angular/src/data/tree-view/recursive-children.ts

@@ -23,7 +23,7 @@ import { TreeFeaturesService } from './tree-features.service';
     </ng-container>
   `,
   host: {
-    '[attr.role]': '"group"', // Safari + VO needs direct relationship between treeitem and group; no element should exist between them
+    '[attr.role]': 'role', // Safari + VO needs direct relationship between treeitem and group; no element should exist between them
   },
 })
 /**
@@ -37,6 +37,7 @@ export class RecursiveChildren<T> {
   @Input('children') children: TreeNodeModel<T>[];
 
   subscription: Subscription;
+  role: string;
 
   constructor(public featuresService: TreeFeaturesService<T>, @Optional() private expandService: IfExpandService) {
     if (expandService) {
@@ -51,6 +52,10 @@ export class RecursiveChildren<T> {
     }
   }
 
+  ngAfterContentInit() {
+    this.setAriaRoles();
+  }
+
   shouldRender() {
     return (
       this.featuresService.recursion &&
@@ -73,4 +78,8 @@ export class RecursiveChildren<T> {
       this.subscription.unsubscribe();
     }
   }
+
+  private setAriaRoles() {
+    this.role = this.parent ? 'group' : null;
+  }
 }