ENH: add support for Qt6 input hooks - #13085

(allqt) PS C:\work> $env:QT_API="pyqt6"
(allqt) PS C:\work> ipython
Python 3.8.10 (tags/v3.8.10:3d8993a, May  3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)]
Type 'copyright', 'credits' or 'license' for more information
IPython 7.27.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: %gui qt

In [2]: Traceback (most recent call last):
# snip
  File "c:\work\venv\allqt\lib\site-packages\IPython\terminal\pt_inputhooks\qt.py", line 67, in inputhook
    event_loop.exec_()
AttributeError: 'QEventLoop' object has no attribute 'exec_'