misc: Port latest Fyne layout changes

Specific commits ported, to update the layouts and reduce differences
with upstream Fyne code:

* https://github.com/fyne-io/fyne/commit/a9a66f60d2167d7945bcf7718a781335541317c0
* https://github.com/fyne-io/fyne/commit/2cde868904092382ca5f645802ee9d444d8ae6e8
* https://github.com/fyne-io/fyne/commit/99fa7e3a7dc83dd273ad366cc7d336a1e1cee5f6
* https://github.com/fyne-io/fyne/commit/4ea8a5762f1744401ede9f7bd35b3b75890f925e

ui/layouts/vboxcustompadding.go

@@ -2,6 +2,7 @@ package layouts
 
 import (
 	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/layout"
 	"fyne.io/fyne/v2/theme"
 )
 
@@ -11,41 +12,76 @@ type VboxCustomPadding struct {
 	ExtraPad float32
 }
 
+func (*VboxCustomPadding) isSpacer(obj fyne.CanvasObject) bool {
+	spacer, ok := obj.(layout.SpacerObject)
+	return ok && spacer.ExpandVertical()
+}
+
 func (v *VboxCustomPadding) MinSize(objects []fyne.CanvasObject) fyne.Size {
 	minSize := fyne.NewSize(0, 0)
+	addPadding := false
+	padding := theme.Padding() + v.ExtraPad
 	for _, child := range objects {
-		if !child.Visible() {
+		if !child.Visible() || v.isSpacer(child) {
 			continue
 		}
 
-		minSize.Width = fyne.Max(child.MinSize().Width, minSize.Width)
-		minSize.Height += child.MinSize().Height
+		childMin := child.MinSize()
+		minSize.Width = fyne.Max(childMin.Width, minSize.Width)
+		minSize.Height += childMin.Height
+		if addPadding {
+			minSize.Height += padding
+		}
+		addPadding = true
 	}
-	minSize.Height += (theme.Padding() + v.ExtraPad) * float32(len(objects)-1)
 	return minSize
 }
 
 func (v *VboxCustomPadding) Layout(objects []fyne.CanvasObject, size fyne.Size) {
+	spacers := 0
+	visibleObjects := 0
+	// Size taken up by visible objects
 	total := float32(0)
+
 	for _, child := range objects {
 		if !child.Visible() {
 			continue
 		}
+
+		if v.isSpacer(child) {
+			spacers++
+			continue
+		}
+
+		visibleObjects++
 		total += child.MinSize().Height
 	}
 
-	x, y := float32(0), float32(0)
-
 	padding := theme.Padding() + v.ExtraPad
-	extra := float32(0)
+
+	// Amount of space not taken up by visible objects and inter-object padding
+	extra := size.Height - total - (padding * float32(visibleObjects-1))
+
+	// Spacers split extra space equally
+	spacerSize := float32(0)
+	if spacers > 0 {
+		spacerSize = extra / float32(spacers)
+	}
+
+	x, y := float32(0), float32(0)
 	for _, child := range objects {
 		if !child.Visible() {
 			continue
 		}
+
+		if v.isSpacer(child) {
+			y += spacerSize
+			continue
+		}
+		child.Move(fyne.NewPos(x, y))
+
 		height := child.MinSize().Height
-		child.Move(fyne.NewPos(x, y+extra))
-		y += height
+		y += padding + height
 		child.Resize(fyne.NewSize(size.Width, height))
-		extra += padding
 	}
 }