Provide support for designing ContentDialog

[nickrandolph]

Discussed in #7

^{Originally posted by sarosigy December 13, 2024}
The title is pretty much the question. How to access Hot Design features when a ContentDialog is open?

First observation: The HotDesign toolbar is not show on the surface of a ContentDialog, and the one on the Main Window is inaccessible, obviously.
Second observation: While Hot Design open, pressing the play and cause to open a ContentDialog in the app, the dialog's overlay and the dialog itself will be over the whole Hot Design surface, and only the ContentDialog can be clicked on, nothing else.