Widget types for unselectable and custom views

Added new constants to be used by custom text view implementions, as well
as a special case for non-selectable text that will only become meaningful
once we start logging linkified text.

Bug: 67674199
Test: Tested that there are no regressions in the existing behaviour.
Change-Id: I0167c39bdbde2783f13a8776d6e280aadf55476b