[schema] improve normalization of RQLExpressions
Parse and print back the expression instead of manipulating the string.
Among other benefits, it means we don't mangle embedded string constants
that contain commas or multiple spaces.
Closes #6694426
from yams.buildobjs import ComputedRelation, EntityType, RelationDefinition
from cubicweb.schema import RRQLExpression
class Subject(EntityType):
pass
class Object(EntityType):
pass
class relation(RelationDefinition):
subject = 'Subject'
object = 'Object'
class computed(ComputedRelation):
rule = 'S relation O'
__permissions__ = {'read': (RRQLExpression('S is ET'),)}