Change `var` to `out` in interface to unbreak examples

[fabric-and-ink]

Some of the example projects do not compile since they implement a different version of the interface IUICommandHandler. This is a breaking change for users of this library.

[joachimmarder]

I think it would make more sense to adjust the samples to this change. Gibe the documentation of this parameter at https://docs.microsoft.com/en-us/windows/desktop/api/uiribbon/nf-uiribbon-iuicommandhandler-updateproperty out makes more sense.

[fabric-and-ink]

Ok!

[SaschaSchaefer]

I changed the parameter back to "out" and adjusted the implementing classes as well.

For some reason I changed it some time ago to var. However, as @joachimmarder noted, "out" makes more sense.