Hiding box menu item button text

[swashbuck]

Subject of the enhancement

Currently, it is difficult to remove the "view" button text and still have the text as part of the aria label.

Use case

Sometimes, we will replace the text with an arrow icon or something similar. However, we still want the aria label to read "View Topic 1".

Possible solutions

1. Wrap the text in .boxmenu-item__button with a span tag that can be hidden with CSS in a custom theme.
2. Add a new property for linkTextAria so that the aria label can be set independently of the linkText value.