Clarify DirectoryNotFoundException behavior for Directory.Move and File.Move destination paths

[Copilot]

Directory.Move docs implied DirectoryNotFoundException was only tied to sourceDirName, which was misleading when destination path segments do not exist. File.Move had similar ambiguity around what makes destFileName invalid.

• Exception contract clarification (System.IO.Directory.Move)

  • Updated DirectoryNotFoundException text to cover invalid paths in either sourceDirName or destDirName.
  • Explicitly calls out missing intermediate directories in destDirName as a triggering condition.

• Exception contract clarification (System.IO.File.Move overloads)

  • Updated both overloads:
    • File.Move(string sourceFileName, string destFileName)
    • File.Move(string sourceFileName, string destFileName, bool overwrite)
  • Clarified that DirectoryNotFoundException includes cases where one or more directories in destFileName do not exist.

• Behavior illustrated

Directory.CreateDirectory("src");
Directory.Move("src", "dst/dst"); // throws DirectoryNotFoundException if "dst" does not exist

File.Move("a.txt", "missing/subdir/a.txt"); // throws DirectoryNotFoundException if "missing/subdir" does not exist