Add grouping and affixation functions for module completion

Add grouping and affixation functions for module completion

This adds a 'group-function' and an 'affixation-function' to
'sweeprolog-module-completion-table', for Emacs 28+

The affixation API allows us to compute the appropriate padding to
insert before annotations in a cleaner way.  Modules are group
according to their classes.

* sweep.pl (sweep_module_class/2): New predicate.

* sweeprolog.el (sweeprolog-module-minibuffer-annotation-1):
Extract helper function from...
(sweeprolog-module-minibuffer-annotation): ...here. Adapt.
(sweeprolog-module-minibuffer-affixation)
(sweeprolog-module-minibuffer-group): New functions.
(sweeprolog-module-completion-table): Use them.