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/file_name_manager.cpp

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <iostream>
+#include <tuple>
+
+#include "flatbuffers/file_manager.h"
+
+namespace flatbuffers {
+
+bool FileNameSaver::SaveFile(const char* name, const char* buf, size_t len,
+                             bool binary) {
+  (void)buf;
+  (void)len;
+  (void)binary;
+
+  std::ignore = file_names_.insert(name);
+
+  // we want to simulate always successful save
+  return true;
+}
+
+void FileNameSaver::Finish() {
+  for (const auto& file_name : file_names_) {
+    // Just print the file names to standard output.
+    // No actual file is created.
+    std::cout << file_name << "\n";
+  }
+}
+
+}  // namespace flatbuffers