Add support for left-right splits on portrait devices

- Add a config to transpose the split such that you can split left/right
  while in portrait.  This is mostly useful for portrait based foldable
  devices.
- Refactors the divider, split layout, and drag and drop to be based on
  this new config vs the configuration orientation

Bug: 291018646
Test: Manual
Flag: enable_left_right_split_in_portrait
Change-Id: I8b3b81f2510457c31ababb2db1b5e4031d6dc17c