op: rename StackOp/Push/Pop to StateOp/Save/Load

The semantics were relaxed in a previous commit; this change renames
to operations accordingly.

API change. Use gofmt to adjust your code accordingly:

gofmt -r 'op.Push(a).Pop() -> op.Save(a).Load()'
gofmt -r 'op.Push(a) -> op.Save(a)'
gofmt -r 'v.Pop() -> v.Load()'
gofmt -r 'op.StackOp -> op.StateOp'

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

widget/image.go

@@ -32,10 +32,10 @@ func (im Image) Layout(gtx layout.Context) layout.Dimensions {
 	w, h := gtx.Px(unit.Dp(wf*scale)), gtx.Px(unit.Dp(hf*scale))
 	cs := gtx.Constraints
 	d := cs.Constrain(image.Pt(w, h))
-	stack := op.Push(gtx.Ops)
+	stack := op.Save(gtx.Ops)
 	clip.Rect(image.Rectangle{Max: d}).Add(gtx.Ops)
 	im.Src.Add(gtx.Ops)
 	paint.PaintOp{}.Add(gtx.Ops)
-	stack.Pop()
+	stack.Load()
 	return layout.Dimensions{Size: d}
 }