go/types: use a typeWriter to write types (cleanup)

This is a port of CL 345890 to go/types.

Change-Id: I98162deaf044b2194b05dc51e6948e227216fc4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/346554
Trust: Robert Findley <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: findleyr

src/go/types/object.go

@@ -430,7 +430,7 @@ func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
 			return
 		}
 		if named, _ := typ.(*Named); named != nil && named.TParams().Len() > 0 {
-			writeTParamList(buf, named.TParams().list(), qf, nil)
+			newTypeWriter(buf, qf).tParamList(named.TParams().list())
 		}
 		if tname.IsAlias() {
 			buf.WriteString(" =")

src/go/types/subst.go

@@ -262,10 +262,9 @@ func instantiatedHash(typ *Named, targs []Type) string {
 	assert(instanceHashing == 0)
 	instanceHashing++
 	var buf bytes.Buffer
-	writeTypeName(&buf, typ.obj, nil)
-	buf.WriteByte('[')
-	writeTypeList(&buf, targs, nil, nil)
-	buf.WriteByte(']')
+	w := newTypeWriter(&buf, nil)
+	w.typeName(typ.obj)
+	w.typeList(targs)
 	instanceHashing--
 
 	// With respect to the represented type, whether a

src/go/types/typelists.go

@@ -59,9 +59,7 @@ func (l *TypeList) String() string {
 		return "[]"
 	}
 	var buf bytes.Buffer
-	buf.WriteByte('[')
-	writeTypeList(&buf, l.types, nil, nil)
-	buf.WriteByte(']')
+	newTypeWriter(&buf, nil).typeList(l.types)
 	return buf.String()
 }