FS: copy lfs_info and implement FS::Stat()

Implement the subset of the functionality to be usable to check if the
file exists or not and check the size of the file.

sim/components/fs/FS.cpp

@@ -163,6 +163,16 @@ int FS::DirDelete(const char* path) {
   //return LFS_ERR_OK;
 }
 
+// check if file exists, if so write file-size into info object
+int FS::Stat(const char* path, lfs_info* info) {
+  if (!std::filesystem::exists(path))
+  {
+    return LFS_ERR_NOENT; // No directory entry
+  }
+  info->size = std::filesystem::file_size(path);
+  return LFS_ERR_OK;
+}
+
 /*
 
     ----------- Interface between littlefs and SpiNorFlash -----------