`headerGroupClasses` is marked as hidden

[ymita]

Description

headerGroupClasses is marked as hidden so that our doc does not show it.

• igniteui-angular version: 7.2.0
• browser: n/a

Steps to reproduce

1. See the source code - https://github.com/IgniteUI/igniteui-angular/blob/master/projects/igniteui-angular/src/lib/grids/column.component.ts#L347-L351

Result

headerGroupClasses is marked as hidden.

Expected result

headerGroupClasses is not marked as hidden.

Attachments

Attach a sample if available, and screenshots, if applicable.