add linux definitions for FileDialogWrapper

src/app/core/platform/file_dialog.cc

@@ -0,0 +1,23 @@
+#include "file_dialog.h"
+
+#if defined(__linux__)
+
+std::string FileDialogWrapper::ShowOpenFileDialog() {
+  return "Linux: Open file dialog";
+}
+
+std::string FileDialogWrapper::ShowOpenFolderDialog() {
+  return "Linux: Open folder dialog";
+}
+
+std::vector<std::string> FileDialogWrapper::GetSubdirectoriesInFolder(
+    const std::string& folder_path) {
+  return {"Linux: Subdirectories in folder"};
+}
+
+std::vector<std::string> FileDialogWrapper::GetFilesInFolder(
+    const std::string& folder_path) {
+  return {"Linux: Files in folder"};
+}
+
+#endif