Revisit gotodeclaration handlers

[hurricup]

It seems that they were implemented incorrectly.

• Handlers should only provide non-referenced targets, referenced should be supplied by the platform
• We should probably have different handlers for different targets with appropriate action names, e.g. Navigate to shadowed variable. Looks like this is not achievable with this. Probably requires additional actions in Go to group.
• We should have proper navigation between declaration and definition of the sub
• We could make a navigation to cfg keywords: last, next and redo