add name_v to reflection API

Summary:
After this diff, we can replace

```
fatal::z_data<member::name>()
```

with

```
member::name_v
```

And eventually get rid of legacy reflection codegen for struct/field names.

Reviewed By: aristidisp

Differential Revision: D89331661

fbshipit-source-id: a0e767fea7ed4101c47b292b94ffd75fbc1be467

Author: Mizuchi

third-party/thrift/src/thrift/lib/cpp2/reflection/reflection.h

@@ -446,7 +446,12 @@ reflected_struct {
    *
    * @author: Marcelo Juchem <marcelo@fb.com>
    */
-  using name = typename Traits::name;
+  using name [[deprecated("Use name_v instead")]] = typename Traits::name;
+
+  /**
+   * A run-time string representing the struct name.
+   */
+  static inline const auto name_v = op::get_class_name_v<type>;
 
   /**
    * An implementation defined type template that provides the appropriate
@@ -559,7 +564,13 @@ struct reflected_struct_data_member {
    *
    * @author: Marcelo Juchem <marcelo@fb.com>
    */
-  using name = typename Traits::name;
+  using name [[deprecated("Use name_v instead")]] = typename Traits::name;
+
+  /**
+   * A run-time string representing the struct field name.
+   */
+  static inline const auto name_v =
+      op::get_name_v<typename Traits::owner, typename Traits::tag>;
 
   /**
    * The type of the data member.

third-party/thrift/src/thrift/test/reflection/fatal_struct_test.cpp

@@ -74,6 +74,7 @@ TEST(FatalStruct, Struct1SanityCheck) {
 
   EXPECT_SAME<struct1, traits::type>();
   EXPECT_SAME<struct1s, traits::name>();
+  EXPECT_EQ("struct1", traits::name_v);
 
   EXPECT_SAME<traits, apache::thrift::try_reflect_struct<struct1, void>>();
   EXPECT_SAME<void, apache::thrift::try_reflect_struct<int, void>>();
@@ -84,6 +85,12 @@ TEST(FatalStruct, Struct1SanityCheck) {
   EXPECT_SAME<field3s, traits::member::field3::name>();
   EXPECT_SAME<field4s, traits::member::field4::name>();
   EXPECT_SAME<field5s, traits::member::field5::name>();
+  EXPECT_EQ("field0", traits::member::field0::name_v);
+  EXPECT_EQ("field1", traits::member::field1::name_v);
+  EXPECT_EQ("field2", traits::member::field2::name_v);
+  EXPECT_EQ("field3", traits::member::field3::name_v);
+  EXPECT_EQ("field4", traits::member::field4::name_v);
+  EXPECT_EQ("field5", traits::member::field5::name_v);
 
   struct1 pod;
   *pod.field0() = 19;