Document how to use varargs in Argument Clinic

[skirpichev]

---

📚 Documentation preview 📚: https://cpython-devguide--1629.org.readthedocs.build/

[skirpichev]

This is a minor correction of closed pr #1277 (now var-positional arguments passed a C array). The rest looks fine for me.

[AA-Turner]

We should mention both the tuple and array converters, they do different things. Notably array results in PyObject * const *args and Py_ssize_t args_length, whereas tuple just passes a regular PyTupleObject.

Also, I found the PR where : object was removed (python/cpython#126560 by @serhiy-storchaka)

[skirpichev]

Also, I found the PR where : object was removed

It's not removed, just an alias for tuple.

[AA-Turner]

A suggested rephrasing to split tuple and array. I've also switched to saying *args instead of emphasising var-positional, the documentation uses *args or starargs, when discussing the feature in the language reference, it seems to be only internal to Clinic to say varpos.

Suggested change

	How to convert var-positional parameter functions
	-------------------------------------------------
	To convert a var-positional parameter function, prepend the parameter name
	with ``*`` and use the the ``array`` converter.
	For example::
	/*[clinic input]
	var_positional_sample
	foo: int
	*args: array
	[clinic start generated code]*/
	The implementation function will receive var-positional arguments as C array
	*args* of :c:type:`PyObject * <PyObject>`. Alternatively, you could use
	``tuple`` converter to pass a regular :c:type:`PyTupleObject` as argument.
	How to convert ``*args`` parameters (starargs / var-positional)
	---------------------------------------------------------------
	There are two converters suitable for ``*args``: *array* and *tuple*.
	Using the *array* converter will provide the implementation function with
	a C array *args* of type of :c:type:`PyObject * <PyObject>` and the number
	of items in the array as :c:type:`Py_ssize_t` *args_length*.
	For example::
	/*[clinic input]
	var_positional_sample
	spam: int
	*args: array
	[clinic start generated code]*/
	Using the *tuple* converter will provide the implementation function with
	a standard :c:type:`PyTupleObject`.
	For example::
	/*[clinic input]
	var_positional_sample
	spam: int
	*args: tuple
	[clinic start generated code]*/

[skirpichev]

IMO, it's too verbose. But OK.