cubicweb #1796804 cleanup base facet api [resolved]

variables ambiguity: * rqlst / select * mainvar / filtered_variable

itou in some function names

functions could be reorganised to be reusable more easily

prioritynormal
typeenhancement
done in3.13.1
load0.300
load left0.000
closed by#48abeac162fd [facets] refactor / cleanup facet api: more consistent variable naming and easier to reuse function. Closes #1796804