layout: include Expanded sizes in Stack size calculation

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

layout/stack_test.go

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package layout
+
+import (
+	"image"
+	"testing"
+)
+
+func TestStack(t *testing.T) {
+	var gtx Context
+	gtx.Reset(nil, image.Point{X: 100, Y: 100})
+	gtx.Constraints.Width.Min = 0
+	gtx.Constraints.Height.Min = 0
+	exp := image.Point{X: 60, Y: 70}
+	Stack{Alignment: Center}.Layout(&gtx,
+		Expanded(func() {
+			gtx.Dimensions.Size = exp
+		}),
+		Stacked(func() {
+			gtx.Dimensions.Size = image.Point{X: 50, Y: 50}
+		}),
+	)
+	if got := gtx.Dimensions.Size; got != exp {
+		t.Errorf("Stack ignored Expanded size, got %v expected %v", got, exp)
+	}
+}