Improved user experience for drop down widgets on touch devices

Before this PR, when selecting an item in the popup of a drop down widget (such as a DatePicker, an AutoComplete, a SelectBox or a MultiSelect), the focus goes back to the input element.

On touch devices, focusing an input element triggers the display of the keyboard. This PR prevents the focus from going back to the input element immediately after selecting an element in the popup of a drop down widget on touch devices or when touching the dropdown icon.

The behavior is not changed on non-touch devices (the detection of touch devices is done through `aria.utils.Device.isTouch`).
I totally agree with the principle of separation of concerns, and having a dedicated span for this feature makes sense.
My concern is indeed about custom style introduced by the user, it might make the span visible (even if it would occur on very strange cases). I think it doesn't cost too much to specify explicitly the style attributes of the span once at its creation, to set a null size. What do you think?