Mobile text selection controls

Summary:
in QQC2 the text selection controls depend upon the style, which has to
implement it by itself
this adds touch based draggable cursor and text selection handles,
alongside a tiny toolbar for cut/copy/paste

the desktop style will need the exact same thing
T10023

Test Plan:
works correctly when in tablet mode, none of this is visible
when in desktop mode where the text fields behave normally

Reviewers: Plasma, bshah

Reviewed By: Plasma, bshah

Subscribers: ngraham, abetts, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D16841