text: Title: Changes in whole_word_jumping xontrib (ptk_win32) break loading under linux
  Body: The changes introduced in #4788 break loading xontrib `whole_word_jumping` under linux.
  
  ## xonfig
  ```
  $ xonfig
  
  +------------------+----------------------+
  | xonsh            | 0.12.5.dev2          |
  | Git SHA          | f077e23b             |
  | Commit Date      | Jun 17 12:53:59 2022 |
  | Python           | 3.10.5               |
  | PLY              | 3.11                 |
  | have readline    | True                 |
  | prompt toolkit   | 3.0.29               |
  | shell type       | prompt_toolkit       |
  | history backend  | sqlite               |
  | pygments         | 2.11.2               |
  | on posix         | True                 |
  | on linux         | True                 |
  | distro           | manjaro              |
  | on wsl           | False                |
  | on darwin        | False                |
  | on windows       | False                |
  | on cygwin        | False                |
  | on msys2         | False                |
  | is superuser     | False                |
  | default encoding | utf-8                |
  | xonsh encoding   | utf-8                |
  | encoding errors  | surrogateescape      |
  | xontrib 1        | cmd_done             |
  | xontrib 2        | prompt_ret_code      |
  | xontrib 3        | fzf-widgets          |
  | xontrib 4        | prompt_bar           |
  | xontrib 5        | xog                  |
  | xontrib 6        | pipeliner            |
  | xontrib 7        | readable-traceback   |
  | RC file 1        | /home/user/.xonshrc  |
  +------------------+----------------------+
  ```
  
  ## Expected Behavior
  Xontrib is loaded as with xonsh 0.12.4.
  
  ## Current Behavior
  Xontrib fails to load with:
  
  ```shell
  AssertionError
  Failed to load xontrib whole_word_jumping.
  ```
  
  ## Steps to Reproduce
  `xontrib load whole_word_jumping`
  
  ## Possible Change
  
  The problem is the import of `prompt_toolkit.input.win32` which is not feasible under Linux. A conditional import might help:
  
  ```python
  from xonsh.platform import ON_WINDOWS
  if ON_WINDOWS:
     import prompt_toolkit.input.win32 as ptk_win32
  ```
  
  