Draft dialog shell usercontrol

[tommy9]

Sets up draft DialogShell user control in line with #56. Tried to make it flexible by looking ahead to the proposed designs of the message box, rename prompt and preview rename prompt. To accommodate the different layouts, the main content section is set as a ContentControl which the various specific view models can define. As an example, the design data file has a code switch to allow previewing either a text block or an input text box.

Issues:

• Wanted to put a ScrollViewer around the TextBlock for the expandable section but was crashing in the VBE so commented out for now
• Scaling not so nice if using a TextBox as the main control as that is the row which takes remaining space, would be fine if setting the overall dialog size appropriately

Not included is a temporary button to show the dialog in the VBE. Sample with dummy data:

[Greedquest]

From a position of zero code reviewing:

Is there a way to make this look more like an office program? Like ui styling that Microsoft uses for host apps, with those classy windows. Having the same design language as ms office would subconsciously put more trust in the ducky I think. But maybe this is hard given VBx hosts span the ages in their own looks.

Or is visual theme not part of this pr and it's more about the kinds of buttons and layout?

[retailcoder]

Or is visual theme not part of this pr and it's more about the kinds of buttons and layout?

Precisely: theming needs to be looked into early on, but this isn't it. I'm happy with whatever works at the moment.