Force kwin to give focus to SMPlayer on "Toggle window media player" (it actually applies to all non-KDE media players using MPRIS)

[kupiqu]

This issue follows some discussion in issue #37

SMPlayer dev comment:

There's already code to raise the window in the mpris2 code (of SMPlayer), however it seems most desktops ignore it because they don't allow a window to go foreground on its own. The dragonplayer uses a specific function from the KDE libraries to do it (KWindowSystem::forceActiveWindow), but I can't use the KDE libraries, otherwise smplayer will depend on a lot of KDE packages.

Maybe the call to that function can be done by playbar2. According to
the KDE documentation that function should only be used by "pagers and
similar tools".

https://api.kde.org/frameworks/kwindowsystem/html/classKWindowSystem.html#aecb213d950a6615fc0e961273d72e166

Thanks for considering!