[igx-combo] required attribute is always set to false

[IvanKitanov17]

Description

When setting the Validators.required in the Angular constructor, the aria-required attribute should change to "true", now it is only false no matter if the component is required or not. Similar to the following issue - #15837.

• igniteui-angular version:
• browser:

Expected result

When setting required the aria-required should correspond to whether the component has required state or not.