AST Viewer selection bounces around #656
Description
When clicking on an entry in the AST viewer, if there is a child entry whose source location is identical to the parent's location, the selected entry will change to the child entry.
The reason is that we do a depth first search of the best tree selection based on current text selection.
Possible solution: when determining which viewer node to select, if two nodes have the same source location, but one is already selected don't change the selection.