... and also convert KDE5FilePicker. And Qt5Frame.

The UNO methods in Qt5FilePicker/KDE5FilePicker have to ensure that the
thread actually owns SolarMutex, because if RunInMainThread() is
called without that it will deadlock.

Change-Id: Ie4d2f494ac81c799ec7c9a3acb3a9b0f77bb6361
Reviewed-on: https://gerrit.libreoffice.org/68357
Tested-by: Jenkins
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>