Close #6481
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Pointed-out-by: Rémi Duraffort <ivoire@videolan.org>

add_callback could not work correctly with the (lack of) Lua threading
support. Fortunately, it was not in use.

del_callback depends on add_callback.

Fixes combo visibility in open_panel

Visibility changes were not applied to the created qwidget
except for base class.
Changes were also not implemented for some classes.

vout_macosx: check whether the receiving window can respond to non-standard calls prior to calling them (close #6034)

If the interface script has nothing to do, then it can simply end and
the let the interface thread finish ahead of pf_deactivate.
This will _not_ automatically cause VLC to exit.

If there is nothing to do, then the interface thread can finish.

The Lua interpreter is not thread-safe. So this API made absolutely no
sense: the timer callback is called asynchronously from another thread.
Fortunately, none of our Lua scripts used this except for testing.

(This should probably be moved to Lua code.)

Pointed-out-by: Edward Wang <edward.c.wang@compdigitec.com>

The function is a bit ugly but it's difficult to do this using
pure arithmetic.

Fixes #6378

Till now, when a tooltip showed up, the underlying main window lost
keyboard focus (keys + mouse wheel). Users had to click again on the window
to regain this focus.

this patch mainly uses a flag that enables to display a window without
activating it (see msdn doc) plus a bit of cosmetics.

this patch should be backported.

Note that all current configcontrol are instanciated using the
existing gridlayout constructor by createConfigControl().
We probably can drop constructors for self contained configcontrols.