Summary:
This change adds a DBus API to query whether the virtual keyboard is
currently enabled and provides DBus methods to request that the virtual
keyboard gets enabled/disabled. This is useful for e.g. providing a
Plasmoid or for convertables where the tablet mode needs to be enabled.

Reviewers: #kwin, #plasma

Subscribers: plasma-devel, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D8166