make servicerunner only build once
Summary:
build the runner itself in a static lib we can use for testing and then
link that into a module lib together with the factory entry point to
compose the final lib for installation
means servicesrunner.cpp is now only built once, whereas before it was
built twice through 100% duplicative targets
Test Plan: test still passes, installing and restarting krunner still yields working service searches
Reviewers: broulik, davidedmundson
Reviewed By: davidedmundson
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28137