cmd/protoc-gen-go: perform some code cleanup

Minor changes:
* Use x as the receiver since "e" and "m" are meaningless in the presence
of user-defined enum and message names.
* Consistently keep enum methods together, rather awkwardly split apart
by the value maps.

Change-Id: I68e5666efb56ac7a4d062fb223b9f826dc72aba9
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/170357
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/cmd/protoc-gen-go/internal_gengo/reflect.go b/cmd/protoc-gen-go/internal_gengo/reflect.go
index 69b5acd..2d0a9ff 100644
--- a/cmd/protoc-gen-go/internal_gengo/reflect.go
+++ b/cmd/protoc-gen-go/internal_gengo/reflect.go
@@ -242,20 +242,29 @@
 func genReflectEnum(gen *protogen.Plugin, g *protogen.GeneratedFile, f *fileInfo, enum *protogen.Enum) {
 	idx := f.allEnumsByPtr[enum]
 	typesVar := enumTypesVarName(f)
-	g.P("func (e ", enum.GoIdent, ") Type() ", protoreflectPackage.Ident("EnumType"), " {")
+
+	// Type method.
+	g.P("func (", enum.GoIdent, ") Type() ", protoreflectPackage.Ident("EnumType"), " {")
 	g.P("return ", typesVar, "[", idx, "]")
 	g.P("}")
-	g.P("func (e ", enum.GoIdent, ") Number() ", protoreflectPackage.Ident("EnumNumber"), " {")
-	g.P("return ", protoreflectPackage.Ident("EnumNumber"), "(e)")
+	g.P()
+
+	// Number method.
+	g.P("func (x ", enum.GoIdent, ") Number() ", protoreflectPackage.Ident("EnumNumber"), " {")
+	g.P("return ", protoreflectPackage.Ident("EnumNumber"), "(x)")
 	g.P("}")
+	g.P()
 }
 
 func genReflectMessage(gen *protogen.Plugin, g *protogen.GeneratedFile, f *fileInfo, message *protogen.Message) {
 	idx := f.allMessagesByPtr[message]
 	typesVar := messageTypesVarName(f)
-	g.P("func (m *", message.GoIdent, ") ProtoReflect() ", protoreflectPackage.Ident("Message"), " {")
-	g.P("return ", typesVar, "[", idx, "].MessageOf(m)")
+
+	// ProtoReflect method.
+	g.P("func (x *", message.GoIdent, ") ProtoReflect() ", protoreflectPackage.Ident("Message"), " {")
+	g.P("return ", typesVar, "[", idx, "].MessageOf(x)")
 	g.P("}")
+	g.P()
 }
 
 func rawDescVarName(f *fileInfo) string {