widget/material: make clickable respect constraints

This change makes material.Clickable propagate the constraints it is
invoked with to the widget being made clickable. Without this, the
internal use of layout.Stack resets the minimum constraints to zero.
This has the confusing effect of breaking a working layout when you
decide to wrap one element in a Clickable, which I think is sufficiently
surprising that we should eliminate the footgun.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/material/button.go

@@ -91,6 +91,7 @@ func IconButton(th *Theme, button *widget.Clickable, icon *widget.Icon, descript
 func Clickable(gtx layout.Context, button *widget.Clickable, w layout.Widget) layout.Dimensions {
 	return button.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
 		semantic.Button.Add(gtx.Ops)
+		constraints := gtx.Constraints
 		return layout.Stack{}.Layout(gtx,
 			layout.Expanded(func(gtx layout.Context) layout.Dimensions {
 				defer clip.Rect{Max: gtx.Constraints.Min}.Push(gtx.Ops).Pop()
@@ -102,7 +103,10 @@ func Clickable(gtx layout.Context, button *widget.Clickable, w layout.Widget) la
 				}
 				return layout.Dimensions{Size: gtx.Constraints.Min}
 			}),
-			layout.Stacked(w),
+			layout.Stacked(func(gtx layout.Context) layout.Dimensions {
+				gtx.Constraints = constraints
+				return w(gtx)
+			}),
 		)
 	})
 }