DialogHost doesn't return current value when dialog is accepted from keyboard.

DialogHost doesn't return current value when dialog is accepted from keyboard.

MaterialDesignThemes v. 4.0.0

Repository with example: https://github.com/lszczygielek/MaterialDesignInXamlToolkit-DialogHost-Focus

@Keboo wrote about it on Gitter:

I wrote a small test to also show the issue here. I did write a little UI test to reproduce the issue as well: https://github.com/Keboo/MaterialDesignInXamlToolkit/tree/dialogHostDoesNotUpdate
If anyone wants to have a go at addressing it that would be a good start. I spent a little time looking at it, and it seems like it may be a little difficult with timing to address it within the dialog host as you need to trigger the lost focus event and wait for the binding to update. This may end up being something that needs to be addressed outside of this library.
It also appears this is somewhat expected as several other people have run into similar use cases. https://www.thomasclaudiushuber.com/2008/05/02/lostfocus-textbox-vs-buttons-isdefault-property/

Beginne mit dem verlinkten DialogHost-Focus-Beispiel und dem UI-Test im Branch dialogHostDoesNotUpdate, um die Bestätigung per Tastatur in MaterialDesignThemes 4.0.0 zu reproduzieren. Verfolge anschließend die Verarbeitung von Fokus und Bindungsaktualisierungen durch DialogHost und überprüfe dann, dass das Bestätigen des Dialogs den aktuell im Steuerelement angezeigten Wert zurückgibt.