A few mini-fixes for the accessibility layout inspector

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

android/src/test/java/com/facebook/flipper/plugins/inspector/InspectorFlipperPluginTest.java

@@ -101,7 +101,9 @@ public class InspectorFlipperPluginTest {
                 .put("children", new FlipperArray.Builder().put("test"))
                 .put("attributes", new FlipperArray.Builder())
                 .put("decoration", (String) null)
-                .put("extraInfo", new FlipperObject.Builder().put("hasAXNode", true))
+                .put(
+                    "extraInfo",
+                    new FlipperObject.Builder().put("linkedNode", "com.facebook.flipper"))
                 .build()));
   }