cubicweb #2186039 eid fallback in entity.rest_path should return <eid> path, not <etype>/eid/<eid> [validation pending]

as this is the form used for cw entities uri

prioritynormal
typebug
done in3.14.5
load0.100
load left0.000
closed by#8b0146e31baa [entity url] rest path fallback should be the url used as cwuri. Closes #2186039