Collecting factors does not take into account anti-commutativity

[kpeeters]

The following does not produce the required minus sign:

{A,X}::AntiCommuting.
ex := X A X;
collect_factors(ex);

First doing sort_product will do the right thing. First reported in https://cadabra.science/qa/2958/collect_factors-simplify-with-anticommuting-objects .