Add default parameter for arguments in start, startDetached, and
execute for better source compatibility with Qt 5.15. This has the risk
of then hiding incorrect calls to the previous overload taking a single
"command" strings if code is ported from pre-5.15 or ignores deprecation
warnings. This is acceptable, given that the alternative is that all
calls to these functions would require a default constructed QStringList
as the second parameter.
Change-Id: I1ba4df97ac4894d007da5083c8359015d784ddbb
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>