gh-104683: Argument clinic: pass clinic as a parameter where possible

[AlexWaygood]

This PR started off life with me wanting to get rid of this at the end of Clinic.__init__, which feels like an awful hack to me:

cpython/Tools/clinic/clinic.py

Lines 2206 to 2207 in d0dcd27

	global clinic
	clinic = self

clinic is elsewhere set to None in the global namespace in two places:

cpython/Tools/clinic/clinic.py

Line 2085 in d0dcd27

clinic = None

cpython/Tools/clinic/clinic.py

Line 5621 in d0dcd27

clinic = None

Unfortunately, removing this hack completely is rather difficult, due to the fact that warn_or_fail relies on clinic being a global variable! Passing clinic as a parameter to warn_or_fail would mean that every usage of warn() or fail() would have to be updated, which would have led to a huge diff.

cpython/Tools/clinic/clinic.py

Lines 155 to 171 in d0dcd27

	def warn_or_fail(
	*args: object,
	fail: bool = False,
	filename: str | None = None,
	line_number: int | None = None,
	) -> None:
	joined = " ".join([str(a) for a in args])
	add, output = text_accumulator()
	if fail:
	add("Error")
	else:
	add("Warning")
	if clinic:
	if filename is None:
	filename = clinic.filename
	if getattr(clinic, 'block_parser', None) and (line_number is None):
	line_number = clinic.block_parser.line_number

Nonetheless, this PR still feels like a (small) improvement over the current state of affairs. In particular, by passing clinic as a parameter to output_templates, we remove the need for an assert clinic is not None assertion. This PR also reduces the changes that will be required in the future, should we want to move output_templates into a separate module...

• Issue: Modernise code in Tools/clinic/ #104683

[erlend-aasland]

Makes sense. Thanks!