[autotest] Add a test case for QtSurfaceExtensionInterface

Summary:
KWayland does not have a client implementation of the QtSurfaceExtension
protocol. Thus the test is different: it starts a helper binary which
creates a QWindow. The test closes that one which should terminate the
started applications.

Reviewers: #plasma

Subscribers: plasma-devel

Projects: #plasma

Differential Revision: https://phabricator.kde.org/D1388