This PR changes exception chaining used in the library from Exception.with_traceback/sys.exc_info to PEP 3134.

There are minor user-visible changes in the exception report:

• the line During handling of the above exception, another exception occurred is replaced with The above exception was the direct cause of the following exception

  Comparison of the full console output

  Before:

  Python 3.11.0a6 (main, Mar  7 2022, 16:46:19) [MSC v.1929 64 bit (AMD64)] on win32
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import urllib.parse
  >>> urllib.parse.urlencode(None)
  Traceback (most recent call last):
    File "C:\Program Files\Python311\Lib\urllib\parse.py", line 937, in urlencode
      if len(query) and not isinstance(query[0], tuple):
         ^^^^^^^^^^
  TypeError: object of type 'NoneType' has no len()
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "C:\Program Files\Python311\Lib\urllib\parse.py", line 945, in urlencode
      raise TypeError("not a valid non-string sequence "
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    File "C:\Program Files\Python311\Lib\urllib\parse.py", line 937, in urlencode
      if len(query) and not isinstance(query[0], tuple):
         ^^^^^^^^^^
  TypeError: not a valid non-string sequence or mapping object
  

  After:

  Python 3.11.0a6+ (main, Mar 23 2022, 12:00:42) [MSC v.1929 64 bit (AMD64)] on win32
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import urllib.parse
  >>> urllib.parse.urlencode(None)
  Traceback (most recent call last):
    File "C:\Users\oleg\Documents\dev\cpython\Lib\urllib\parse.py", line 937, in urlencode
      if len(query) and not isinstance(query[0], tuple):
         ^^^^^^^^^^
  TypeError: object of type 'NoneType' has no len()
  
  The above exception was the direct cause of the following exception:
  
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "C:\Users\oleg\Documents\dev\cpython\Lib\urllib\parse.py", line 944, in urlencode
      raise TypeError("not a valid non-string sequence "
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  TypeError: not a valid non-string sequence or mapping object
  

• all URLError exception messages raised in urllib.request.URLopener now contain a colon between ftp error and the rest of the message. Previously, URLopener.open_ftp() missed the colon.

https://bugs.python.org/issue47099