RFR: JDK-8297047: IGV: graphContent not set when opening a new tab

[Tobias Holenstein]

Open any graph in IGV. The graph will be opened in a new tab as expected. But the tab has the name "graph" instead of the actual graph name. Further, the "Bytecode" and "Control Flow" windows are not updated with the current graph. 

The reason was that `graphContent` was not set when opening a new EditorTopComponent.

Before: 
![graph_not_updated](https://user-images.githubusercontent.com/71546117/201946772-727f1c57-d69e-4551-a560-14d18cfb2b63.png)

Now the title of tab and the "Control Flow" is updated:
![graph_updated](https://user-images.githubusercontent.com/71546117/201947659-a238d0a2-b064-4373-81dc-7fb3f0dea7ec.png)

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Commit messages:
 - JDK-8297047: IGV: graphContent not set when opening a new tab

Changes: https://git.openjdk.org/jdk/pull/11168/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11168&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297047
  Stats: 13 lines in 1 file changed: 8 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11168.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11168/head:pull/11168

PR: https://git.openjdk.org/jdk/pull/11168