refactor(cell, header): use headerCell.id for aria-describedby

Author: ddaribo

projects/igniteui-angular/src/lib/grids/headers/grid-header.component.ts

@@ -55,6 +55,13 @@ export class IgxGridHeaderComponent implements DoCheck, OnDestroy {
     @ViewChild('sortIconContainer', { read: ElementRef })
     protected sortIconContainer: ElementRef;
 
+    /**
+     * @hidden
+     */
+    @Input()
+    @HostBinding('attr.id')
+    public id: string;
+
     /**
      * Returns the `aria-selected` of the header.
      */