[Interest] QML: support both Qt5 and Qt6

[Mitch Curtis]

MessageDialog was added in 5.8 according to https://doc.qt.io/qt-5/qml-qt-labs-platform-messagedialog.html, so it should work.

> -----Original Message-----
> From: Alexander Dyagilev <alervdvcw at gmail.com>
> Sent: Thursday, 9 September 2021 10:59 AM
> To: Mitch Curtis <mitch.curtis at qt.io>; Shawn Rutledge
> <Shawn.Rutledge at qt.io>; Qt Interest <interest at qt-project.org>
> Subject: Re: [Interest] QML: support both Qt5 and Qt6
> 
> Hello,
> 
> 5.12.11 :)
> 
> On 9/9/2021 10:18 AM, Mitch Curtis wrote:
> > Which Qt 5 version are you using?
> >