touchscreen text controls

Summary:
on QQC2 the controls to be able to select, cut,copy and paste text are
responsibility of the style.
this enables onscreen text manipulation when the system is in tabletMode
state, just as D16841 for Plasma style

Test Plan:
they work when kirigami is in tablet mode, they are completely invisible when not
and the system behaves completely desktop-like

Reviewers: Plasma, apol

Reviewed By: apol

Subscribers: apol, broulik, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D16860