JsonScalarExpression does not get visited properly in SqlNullabilityProcessor

[roji]

Current implementation of VisitJsonScalar (code):

protected virtual SqlExpression VisitJsonScalar(
    JsonScalarExpression jsonScalarExpression,
    bool allowOptimizedExpansion,
    out bool nullable)
{
    nullable = jsonScalarExpression.IsNullable;

    return jsonScalarExpression;
}

Since we don't visit the Json expression inside JsonScalarExpression, stuff like EF.Constant() isn't applied.

/cc @cincuranet