Debugger info widget should offer to show expressions that cannot be evaluated properly

[xusheng6]

Right now the debugger info widget only shows those expressions that can be evaluated and get a value from. This might be desirable in many cases, but we should also offer an option to list all relevant expressions even if some of them cannot be evaluated. Main motivation:

1. People expect to see the expression there. If they do not see it, they get puzzled. If the expression is listed by with no value, then people understand it cannot be evaluated
2. It would be easier for developers to see some expressions cannot be evaluated and try to figure out why
3. Once Debugger info widget should also show the storage of variable when relevant #635 is done, even if the value cannot be evaluated, people can see the storage of the expression (which should be available and accurate in almost all cases), and then understand why the expression cannot be evaluated