gh-122688: Fix support of var-positional parameter in Argument Clinic (GH-122689)

gh-122688: Fix support of var-positional parameter in Argument Clinic (GH-122689)

* Parameters after the var-positional parameter are now keyword-only
  instead of positional-or-keyword.
* Correctly calculate min_kw_only.
* Raise errors for invalid combinations of the var-positional parameter
  with "*", "/" and deprecation markers.