Properly implementing jump to definition for indexes

[jdbaldry]

For objects, indexes are expressions that must evaluate to a string. For arrays, indexes are expressions that must evaluate to an integer. I think it is safe to assume that a developer would only issue "jump to definition" on a simple index expression. For example, the identifier in target.identifier, the 'string' in target['string'], or the integer in target[integer]. However, the target itself could be an expression as the contrived example (if true then x else y).index.

Those expressions would need to be evaluated and so would all fields and elements of all objects and arrays that may be the definition of the index at point.

Maybe the solution would involve jumping based upon the concrete values in https://github.com/google/go-jsonnet/blob/master/value.go?