fix(a11y): datagrid - invalid aria-attributes in manage column (#1684)

## 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?
Fix for Accessibility issues
<!-- Please check the one that applies to this PR using "x". -->

- [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?
`aria-expanded` property is not added to the element since default value
is set to undefined. Without this property, `aria-controls` and
`aria-owns` will be an invalid property.

<!-- Please describe the current behavior that you are modifying, or
link to a relevant issue. -->

Issue Number: CDE-2542, VPAT-28111

## What is the new behavior?
Added aria-haspopup attribute and aria-expanded property set to false by
default.

## Does this PR introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this PR contains a breaking change, please describe the impact
and migration path for existing applications below. -->

## Other information

projects/angular/src/data/datagrid/datagrid-column-toggle.ts

@@ -31,8 +31,8 @@ import { ColumnsService } from './providers/columns.service';
       clrPopoverAnchor
       clrPopoverOpenCloseButton
       [attr.aria-controls]="popoverId"
-      [attr.aria-owns]="popoverId"
       [attr.aria-expanded]="openState"
+      [attr.aria-haspopup]="'menu'"
     >
       {{ commonStrings.keys.pickColumns }}
     </button>
@@ -83,7 +83,7 @@ import { ColumnsService } from './providers/columns.service';
 })
 export class ClrDatagridColumnToggle implements OnDestroy {
   popoverId = uniqueIdFactory();
-  openState: boolean;
+  openState = false;
 
   // Smart Popover
   smartPosition: ClrPopoverPosition = {