Improve setGroupFocusHighlight

[jessegreenberg]

From an old TODO in the code.

1. We want to expand the groupFocusHighlight so that it can support the same types as focusHighlight.
2. Consider supporting more than one group focus highlight at a time (multiple targets in the Trail)

But not a high priority for now.

[jessegreenberg]

Consider supporting more than one group focus highlight at a time (multiple targets in the Trail)

I do not think we should support this.

In this example, a groupFocusHighlight: true is on the ComboBoxListBox and also the entire panel. The group highlight on the panel shows that it is interactive while subcomponents have focus. But when the ComboBox is open, the panel is not interactive. And in my opinion having several group focus highlights displayed would be more confusing and even poor accessibility.