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/measure/measure.go

@@ -234,7 +234,8 @@ func textPath(ppem fixed.Int26_6, f *opentype, str text.String) ui.MacroOp {
 	builder.Init(ops)
 	var x fixed.Int26_6
 	var advIdx int
-	ops.Record()
+	var m ui.MacroOp
+	m.Record(ops)
 	for _, r := range str.String {
 		if !unicode.IsSpace(r) {
 			segs, ok := f.LoadGlyph(ppem, r)
@@ -287,5 +288,6 @@ func textPath(ppem fixed.Int26_6, f *opentype, str text.String) ui.MacroOp {
 		advIdx++
 	}
 	builder.End()
-	return ops.Stop()
+	m.Stop()
+	return m
 }