RFR: 8263385: IGV: Graph is not opened in the window that has focus.

[Koichi Sakata]

This pull request enables IGV opens a graph in the window that is focused.

At the moment IGV opens a graph in the window that has the graph and is found first. So in this pull request I used preferentially the active EditorTopComponent.

I tested the following scenarios manually:

1. Open a graph, open clone, then open another graph (as described in the bug report). It replaces the clone graph with the last opened graph.
2. Open a graph, open clone, swap tabs by dragging the clone graph, then open another graph. It replaces the clone graph with the last opened graph.
3. Open a graph, open clone, change the focus from the clone graph to the first graph, then open another graph. It replaces the first graph with the last opened graph.
4. Open a graph, open clone, open the same graph xml file from the toolbar, open a graph in the second folder, then open a graph in the first folder. It replaces the leftmost graph that was opened the first with the last opened graph.

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Commit messages:
 - Load a graph to the active top comonent if the active component has the graph

Changes: https://git.openjdk.java.net/jdk/pull/4078/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4078&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263385
  Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4078.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4078/head:pull/4078

PR: https://git.openjdk.java.net/jdk/pull/4078