Add prompt toolkit 3 compatibility to ipdb

[Carreau]

closes #11962
closes #11975

[JBKahn]

@Carreau I'm not sure I understand the fix put in place enough to understand if this is an issue with ipdb or iPython or my system

In this code you modified:

ipython/IPython/terminal/debugger.py

Lines 24 to 70 in 5baea62

	class TerminalPdb(Pdb):
	"""Standalone IPython debugger."""
	def __init__(self, *args, **kwargs):
	Pdb.__init__(self, *args, **kwargs)
	self._ptcomp = None
	self.pt_init()
	def pt_init(self):
	def get_prompt_tokens():
	return [(Token.Prompt, self.prompt)]
	if self._ptcomp is None:
	compl = IPCompleter(shell=self.shell,
	namespace={},
	global_namespace={},
	parent=self.shell,
	)
	self._ptcomp = IPythonPTCompleter(compl)
	kb = KeyBindings()
	supports_suspend = Condition(lambda: hasattr(signal, 'SIGTSTP'))
	kb.add('c-z', filter=supports_suspend)(suspend_to_bg)
	if self.shell.display_completions == 'readlinelike':
	kb.add('tab', filter=(has_focus(DEFAULT_BUFFER)
	& ~has_selection
	& vi_insert_mode | emacs_insert_mode
	& ~cursor_in_leading_ws
	))(display_completions_like_readline)
	options = dict(
	message=(lambda: PygmentsTokens(get_prompt_tokens())),
	editing_mode=getattr(EditingMode, self.shell.editing_mode.upper()),
	key_bindings=kb,
	history=self.shell.debugger_history,
	completer=self._ptcomp,
	enable_history_search=True,
	mouse_support=self.shell.mouse_support,
	complete_style=self.shell.pt_complete_style,
	style=self.shell.style,
	color_depth=self.shell.color_depth,
	)
	if not PTK3:
	options['inputhook'] = self.inputhook
	self.pt_app = PromptSession(**options)

It accesses self.inputhook but Pdb and TerminalPdb don't seem to have an inputhook. At least I get an AttributeError trying to access self.inputhook