RFR: 8294066: IGV: Graph changes when deleting a graph in the same group with smaller index

[Koichi Sakata]

IGV displays a different graph when removing a graph that has a smaller index than the graph displayed in the window. We can reproduce this behavior with the following steps.

1. Open a graph file. Open a graph.
2. In the outline window, remove a graph that has a smaller index than the open graph.
3. The graph changes from the open graph to another graph.

With this pull request, IGV will keep the same graph when doing the above.

# Tests
There are no test classes corresponding to the classes this PR changes. So I did manual tests.

I open the graph at index 8, a diff graph that contains this graph, a graph that clones this graph, and a graph that is in a different folder.

<img width="650" alt="スクリーンショット_20230125_171428" src="https://user-images.githubusercontent.com/60008/214519649-a2e40f77-7ca8-42af-bd64-65f72f53d2cb.png">

I remove the graph at index 1. IGV still shows the same charts and the index of the chart changes from 8 to 7. This affects not only a single graph, but also diff graphs and clone graphs. The graph in another folder, which is "12. Global code motion...",  is not affected.

<img width="650" alt="スクリーンショット_20230125_171457" src="https://user-images.githubusercontent.com/60008/214519675-3e0262b7-86b3-4163-b059-7bd207373e65.png">

Next, I remove the graph at index 10. Its index is greater than the index of the display graph. This time, the diff graph contains the graph at index 12. So the index has changed from 12 to 11.

<img width="650" alt="スクリーンショット_20230125_171528" src="https://user-images.githubusercontent.com/60008/214519713-e5f898f1-5ab5-4fec-bc8c-c5869f50443f.png">

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Commit messages:
 - Make code more simple
 - Keep graphs of other groups as it is
 - Show same graph when removing a graph that has a smaller index

Changes: https://git.openjdk.org/jdk/pull/12210/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12210&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294066
  Stats: 31 lines in 1 file changed: 31 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12210.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12210/head:pull/12210

PR: https://git.openjdk.org/jdk/pull/12210