Allow creating TextBox or SuggestionPopup when extending VFilterSelect (#12491)

This patch adds two methods, that one can override when extending VFilterSelect.
By doing so, the developer can for example change the behavior of setting text,
or performing clicks in the suggestion popup.
This change is backwards compatible, as it just offers two new methods to
override.

Change-Id: Icc8fd154ef1abaed96e6af742af77c3225db3fe4