Summary: - fix mutual selection of elements in ax and non-ax tree (simplifies linkedNode logic as well) - remove unneeded extraInfo attributes (focused, nonAXwithAXchild, & hasAXNode were not/no longer being used) - use 50/50 fixed width view for trees when both are visible Reviewed By: jknoxville Differential Revision: D16390355 fbshipit-source-id: bbf9ea887f8f1035df8b4b0562ddcc4de291f004