Bug with Wayland plus Qt for autocompletion and calltips

[Neil]

[Branched from the "Decreasing seams in scaled windows" thread]

> There is a further problem with current Ubuntu+Wayland in that the windows for autocompletion and calltips fail as they do not have an owning window as their transientParent. 

This is now fixed in the repository with https://sourceforge.net/p/scintilla/code/ci/c105229352ea0d14ee483003ba8c8836bcd258f1/ .

It turns out that setTransientParent can be called inside the showEvent of a QWidget and that makes the popup appear successfully.

Please report any bugs with this change.

Neil