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/border.go

@@ -24,7 +24,7 @@ func (b Border) Layout(gtx layout.Context, w layout.Widget) layout.Dimensions {
 	dims := w(gtx)
 	sz := dims.Size
 	rr := float32(gtx.Px(b.CornerRadius))
-	st := op.Push(gtx.Ops)
+	st := op.Save(gtx.Ops)
 	width := gtx.Px(b.Width)
 	clip.Border{
 		Rect: f32.Rectangle{
@@ -35,6 +35,6 @@ func (b Border) Layout(gtx layout.Context, w layout.Widget) layout.Dimensions {
 	}.Add(gtx.Ops)
 	paint.ColorOp{Color: b.Color}.Add(gtx.Ops)
 	paint.PaintOp{}.Add(gtx.Ops)
-	st.Pop()
+	st.Load()
 	return dims
 }