Reuse ProcessReaper inside process launcher.
Automatically reap all internal QProcesses of QtcProcess
(either direct child of QtcProcess in QProcessImpl
or indirectly inside process launcher).
Make ProcessReaper work again on QProcess instead of on
QtcProcess, so it may still be reused for non-QtcProcesses.
Change-Id: I950cac5cec28f17ae97fe474d6a4e48c01d6aaa2
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>
