cubicweb #6694426 fix normalization of rql expressions [validation pending]

this should be done with a round-trip through rql.parse and as_string not a clumsy string manipulation.

prioritynormal
typebug
done in3.22.0
load1.000
load left0.000
closed by#42c5bd7286b7 [schema] improve normalization of RQLExpressions
patch[schema] improve normalization of RQLExpressions [applied]