Tests: Add standalone test configuration preamble

Add the boilerplate standalone test prelude to each test, so that
they can be configured with cmake or qt-cmake directly without the
qt-cmake-standalone-test script.

Task-number: QTBUG-93020
Change-Id: I0636cdd2d0a201822a52cf2cf03ad1a721a6d564
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>