ui: rename ops to have Op suffixed, not prefixed

Match Go's FooError name pattern.

While we're here, rename RedrawOp to InvalidateOp.

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

ui/text/measure.go

@@ -35,7 +35,7 @@ type Layout struct {
 
 type Face interface {
 	Layout(str string, singleLine bool, maxWidth int) *Layout
-	Path(str String) ui.OpBlock
+	Path(str String) ui.BlockOp
 }
 
 type Alignment uint8