onFocus method
Implementation
@visibleForTemplate
@HostListener('focus')
void onFocus(Event event) {
// Use the focus event to style the element so that when the element is
// styled programmatically it will obey the last known state of the
// directive.
if (_lastInteraction == _InteractionType.mouse) {
hideOutline();
} else {
resetOutline();
}
}