improve accessibility by providing metadata for UI elements
Summary: Add metadata while preserving the string freeze to help a screen reader when navigating with keyboard
Test Plan: Tested under plasma with orca
Reviewers: Elisa, Plasma Accessibility, chempfling, ngraham
Reviewed By: Elisa, Plasma Accessibility, chempfling, ngraham
Subscribers: lavender, davidedmundson, ngraham
Differential Revision: https://phabricator.kde.org/D21608