encoding/textpb: move test protos under encoding/testprotos

These test proto definitions will be reused for encoding/jsonpb package
and hence move these one directory up.

Also, add and simplify some tests.

Change-Id: I5297546fd9b853a7fd3e72dfab2fdc7237332c9c
Reviewed-on: https://go-review.googlesource.com/c/162537
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/encoding/textpb/other_test.go b/encoding/textpb/other_test.go
index 4200ac1..80babd2 100644
--- a/encoding/textpb/other_test.go
+++ b/encoding/textpb/other_test.go
@@ -5,15 +5,14 @@
 
 	protoV1 "github.com/golang/protobuf/proto"
 	"github.com/golang/protobuf/v2/encoding/textpb"
-	"github.com/golang/protobuf/v2/encoding/textpb/testprotos/pb2"
+	"github.com/golang/protobuf/v2/internal/impl"
+	"github.com/golang/protobuf/v2/internal/scalar"
 	"github.com/golang/protobuf/v2/proto"
 	preg "github.com/golang/protobuf/v2/reflect/protoregistry"
 
 	// The legacy package must be imported prior to use of any legacy messages.
 	// TODO: Remove this when protoV1 registers these hooks for you.
-	"github.com/golang/protobuf/v2/internal/impl"
 	_ "github.com/golang/protobuf/v2/internal/legacy"
-	"github.com/golang/protobuf/v2/internal/scalar"
 
 	anypb "github.com/golang/protobuf/ptypes/any"
 	durpb "github.com/golang/protobuf/ptypes/duration"
@@ -21,6 +20,7 @@
 	stpb "github.com/golang/protobuf/ptypes/struct"
 	tspb "github.com/golang/protobuf/ptypes/timestamp"
 	wpb "github.com/golang/protobuf/ptypes/wrappers"
+	"github.com/golang/protobuf/v2/encoding/testprotos/pb2"
 )
 
 func TestRoundTrip(t *testing.T) {