all: remove use of deprecated NewMessage

Replace NewMessage calls with NewField, NewElement, or NewValue.

Change-Id: I6d2bb4f11f0eb2ba7a52308b1addb111137ad4b9
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/193266
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/internal/impl/message_reflect_test.go b/internal/impl/message_reflect_test.go
index de73ff9..a836c89 100644
--- a/internal/impl/message_reflect_test.go
+++ b/internal/impl/message_reflect_test.go
@@ -1326,9 +1326,9 @@
 				v.Append(e)
 			}
 		case appendMessageList:
-			m := v.NewMessage()
-			v.Append(V(m))
-			testMessage(t, p, m, messageOps(op))
+			e := v.NewElement()
+			v.Append(e)
+			testMessage(t, p, e.Message(), messageOps(op))
 		case truncList:
 			v.Truncate(int(op))
 		default:
@@ -1380,7 +1380,7 @@
 			for k, tt := range op {
 				mk := V(k).MapKey()
 				if !m.Has(mk) {
-					m.Set(mk, V(m.NewMessage()))
+					m.Set(mk, m.NewValue())
 				}
 				testMessage(t, p, m.Get(mk).Message(), tt)
 			}