The dialog's presentation mode.
When set to adw.types.DialogPresentationMode.Auto, the dialog appears as a bottom sheet when the following condition is met: max-width: 450px or max-height: 360px, and as a floating window otherwise.
Set it to adw.types.DialogPresentationMode.Floating or adw.types.DialogPresentationMode.BottomSheet to always present it a floating window or a bottom sheet respectively, regardless of available size.
Presentation mode does nothing for dialogs presented as a window.
Builder instance for fluent chaining
Set presentationMode property.