- Moves fs.rename functions to fs.renameAbsolute to match other functions outside of fs.Dir
- Adds fs.Dir.rename that takes two paths relative to the given Dir
- Adds fs.rename that takes two separate Dir's that the given paths are relative to (for renaming across directories without having to make the second path relative to a single directory)
- Fixes FileNotFound error return in std.os.windows.MoveFileExW
- Returns error.RenameAcrossMountPoints from renameatW
  + Matches the RenameAcrossMountPoints error return in renameatWasi/renameatZ