ui: move macro recording from Ops to MacroOp

Move the Record and Stop methods from Ops to MacroOp itself.

Before this change, Ops.Stop stopped the recording of the most
recent macro, which could be a different macro than intended.
After this change, there is no such confusion.

As a bonus, the Ops API becomes less cluttered.

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

ui/layout/layout.go

@@ -119,6 +119,7 @@ func UniformInset(v ui.Value) Inset {
 type Align struct {
 	Alignment Direction
 
+	macro ui.MacroOp
 	ops   *ui.Ops
 	begun bool
 	cs    Constraints
@@ -131,7 +132,7 @@ func (a *Align) Begin(ops *ui.Ops, cs Constraints) Constraints {
 	a.begun = true
 	a.ops = ops
 	a.cs = cs
-	ops.Record()
+	a.macro.Record(ops)
 	cs.Width.Min = 0
 	cs.Height.Min = 0
 	return cs
@@ -143,7 +144,7 @@ func (a *Align) End(dims Dimens) Dimens {
 	}
 	a.begun = false
 	ops := a.ops
-	macro := ops.Stop()
+	a.macro.Stop()
 	sz := dims.Size
 	if sz.X < a.cs.Width.Min {
 		sz.X = a.cs.Width.Min
@@ -166,7 +167,7 @@ func (a *Align) End(dims Dimens) Dimens {
 	}
 	ui.PushOp{}.Add(ops)
 	ui.TransformOp{Transform: ui.Offset(toPointF(p))}.Add(ops)
-	macro.Add(ops)
+	a.macro.Add(ops)
 	ui.PopOp{}.Add(ops)
 	return Dimens{
 		Size:     sz,