name changed notifications for static text widgets

This MR fixes the issue where a change of a label's/inscription's text did not emit a name change notification to assistive technologies. That could cause the ATs to report stale information, if they cached the names, which, for example, Orca wants to do as much as possible. It was inspired by nautilus#3253 (comment 1966603) which was fixed in a different way, but this issue might appear anywhere else.