function onPointerDown(e) {
    if (hadKeyboardEvent === true) {
      removeAllFocusVisibleAttributes();
    }

    hadKeyboardEvent = false;
  }
If at any point a user clicks with a pointing device, ensure that we change
the modality away from keyboard.
This avoids the situation where a user presses a key on an already focused
element, and then clicks on a different element, focusing it with a
pointing device, while we still think we're in keyboard modality.
It also avoids the situation where a user presses on an element within a
previously keyboard-focused element (i.e., `e.target` is not the previously
focused element, but one of its descendants) and we need to remove the
focus ring because a `blur` event doesn't occur.