Linked inspectors should inspect variable, not object

[martinmcclure]

Inspector panes can be independent, or linked from

• A field for a variable in another inspector pane
• A field for a temporary variable in a debugger frame pane
• The result of evaluation in an evaluator sub-pane

Currently, an inspector pane linked from a variable inspects the object referenced by that variable at the time of the pane's opening. If the variable is assigned to reference a different object, the inspector pane linked to that variable closes.

It would be more useful if instead of being tied to the identity of the object, linked inspectors were tied to the variable. Instead of closing when the variable was assigned, they could update to inspect the new object.

Independent inspectors, those not linked to anything, would continue to inspect the object.