EnablePlacementPersistence should be the default without any developer modification

[eduardobragaxz]

WinAppSDK 1.7 Experimental 3 introduced some much needed new windowing APIs, one of them being EnablePlacementPersistence. Since they haven't been brought to Preview 1 I'm assuming they won't be coming in 1.7. Or maybe they'll show up in Preview 2...? I don't know.

I do think that the behavior achieved with this API using the PlacementPersistenceBehaviorFlags.Default enum value should be the default since I'm pretty sure it's the basic windowing behavior developers expect when creating new windows. This feels like the much more sane default.
A GUID could be generated automatically for each new window, maybe exposed with a new property like AppWindow.GUID for whatever reason.

Then, if the developer doesn't need to do anything else with the window, the only thing they need to actually set is if the window is the main window. AppWindow.IsMainWindow.