[rqlrewrite] Enhance detection of need for Exists node We actually want one only if this is not a (`And` / `Or`) binary tree of `Not` or `Exists` nodes, so write a recursive function to tell so. Related to #17074119

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))