Draft: Port from Qt5-only QTEST_MAIN_IMPL to Q6's QTEST_MAIN_WRAPPER

Reverted and reapplied the commit in top of the (current) branch work/igor/kf6 for review purposes.

Picked up review from kdevelop/kdevelop!595 (comment 992426) (reverted the args to restore old order).

Only tested as human reader by manually unrolling the macros ;) No insight into the need and matter and whether the new macro harms the idea.

@mwolff You introduced the usage of those macros in e306f3e3. Could you give this a check?