widget: change Enum.Layout to follow layout protocol

Respect constraints and return dimensions.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/material/radiobutton.go

@@ -37,6 +37,7 @@ func RadioButton(th *Theme, group *widget.Enum, key, label string) RadioButtonSt
 // Layout updates enum and displays the radio button.
 func (r RadioButtonStyle) Layout(gtx layout.Context) layout.Dimensions {
 	dims := r.layout(gtx, r.Group.Value == r.Key)
+	gtx.Constraints.Min = dims.Size
 	r.Group.Layout(gtx, r.Key)
 	return dims
 }