WeldValueExpression must override methods isReadOnly and isLiteralText.

WeldValueExpression must override other methods of ancestor ForwardingValueExpression to push a new CreationalContextCallable() in ELCreationalContextStack.
If it wasn´t done, it will throw IllegalStateException("No CreationalContext registered for EL evaluation, it is likely that the the expression factory has not been wrapped by the CDI BeanManager, which must be done to use the ELResolver from CDI").