text: Title: Process: Kill process if Robot's timeout occurs when waiting for process to end
  Body: Issue #5345 reported that Robot's timeouts weren't able to stop `Run Process` or `Wait For Process` keywords. That was fixed so that these keywords can be stopped, but processes that keywords were waiting for were left running. Leaving process on background especially is likely not a good idea, especially because they often have hung in this case. This issue proposes killing the processes instead.
  
  Killing processes if Robot's timeout occur requires handling the timeout in the library code. That is actually surprisingly easy by catching `robot.errors.TimeoutError` and re-raising it once the process has been killed. There could be other libraries that want to do such cleanup as well, and documenting how to do that in the User Guide is probably a good idea. I'll submit a separate issue about that.
  
  Notice that killing process as proposed above doesn't fully prevent processes to be left running. That can still happen if you use `Start Process` and Robot's timeout occurs before `Wait For Process` is called. We could enhance the library by adding some kind of auto-closing functionality to it, but I don't consider that too high priority because the library already has `Terminate All Processes` that can be used in test or suite teardown. Such an enhancement should anyway get its own issue.