Accessibility Issue fixes for the MenuList Header Items

[shrivastavaajit]

Fixes #
Work Item: W-13840369

Additional description

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[salesforce-cla]

Thanks for the contribution! It looks like @shrivastavaajit is an internal user so signing the CLA is not required. However, we need to confirm this.

[interactivellama]

@shrivastavaajit Thanks for looking into fixing this.

The best fix is present in the component blueprints. Please update to that.
https://v1.lightningdesignsystem.com/components/menus/#With-Subheaders

 <ul role="group" aria-labelledby="menu-group-id-9">
          <li class="slds-dropdown__header slds-truncate" title="Menu Sub Heading" role="presentation" id="menu-group-id-9">
            <span>Menu Sub Heading</span>
          </li>
          <li class="slds-dropdown__item" role="presentation">
            <a href="#" role="menuitem">
              <span class="slds-truncate" title="Menu Item One">Menu Item One</span>
            </a>
          </li>
          <li class="slds-dropdown__item" role="presentation">
            <a href="#" role="menuitem">
              <span class="slds-truncate" title="Menu Item Two">Menu Item Two</span>
            </a>
          </li>
        </ul>
      </li>

I'm unsure about the aria-label on the separator have a heading-like relationship with the list items, since when the menu opens, the first item is selection and not the heading. I'm unsure how the assistive text user would ever hear the separator. What are you finding when you run NVDA?

From a coding perspective, if we introduce nested lists then the updated nested unordered lists might require changes to menu list to get the additional role="group" in there. We'd also need to close the list when the second header is present. https://github.com/salesforce/design-system-react/blob/master/components/utilities/menu-list/index.jsx#L106

I looked at the Lightning Components and it looks like this same issue might be a bug in their library still, too. https://developer.salesforce.com/docs/component-library/bundle/lightning-menu-subheader/example

[interactivellama]

Approved.

[interactivellama]

Approved.

[interactivellama]

@shrivastavaajit Thank you for your contribution!

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