text: convert clip.Ops to op.CallOp

MacroOp is about to lose the ability to run a different operation list
than the one it was recorded on. Text shape caches rely on that property,
and must use the new CallOp operation added for purpose.

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

text/text.go

@@ -3,7 +3,7 @@
 package text
 
 import (
-	"gioui.org/op/clip"
+	"gioui.org/op"
 	"gioui.org/unit"
 	"golang.org/x/image/font"
 	"golang.org/x/image/math/fixed"
@@ -60,7 +60,7 @@ type Font struct {
 // Face implements text layout and shaping for a particular font.
 type Face interface {
 	Layout(ppem fixed.Int26_6, str string, opts LayoutOptions) *Layout
-	Shape(ppem fixed.Int26_6, str String) clip.Op
+	Shape(ppem fixed.Int26_6, str String) op.CallOp
 	Metrics(ppem fixed.Int26_6) font.Metrics
 }