Implement --file-names-only (#8788)

* flatc builds and seems to work, some of the extra targets are having linker errors

* fix build system

* pipeline failures

* un-rename files

* refactor to use unique_ptr

* typo

* rm make_unique, add comments

* fix cmake

---------

Co-authored-by: Wouter van Oortmerssen <aardappel@gmail.com>

src/idl_gen_lobster.cpp

@@ -403,8 +403,9 @@ class LobsterGenerator : public BaseGenerator {
       auto& struct_def = **it;
       GenStruct(struct_def, &code);
     }
-    return SaveFile(GeneratedFileName(path_, file_name_, parser_.opts).c_str(),
-                    code, false);
+    return parser_.opts.file_saver->SaveFile(
+        GeneratedFileName(path_, file_name_, parser_.opts).c_str(), code,
+        false);
   }
 
  private: