RFR: 8288480: IGV: toolbar action is not applied to the focused graph

[Roberto Castañeda Lozano]

When multiple graphs are displayed simultaneously in split windows, the following toolbar actions are always applied to the same graph, regardless of which graph window is focused:

- search nodes and blocks
- extract node
- hide node
- show all nodes
- zoom in
- zoom out

This changeset ensures that each of the above actions is only applied within its corresponding graph window. This is achieved by applying the actions to the graph window that is currently activated (`EditorTopComponent.getRegistry().getActivated()`) instead of the first matching occurrence in `WindowManager.getDefault().getModes()`.

The changeset makes it practical, for example, to explore different views of the same graph simultaneously, as illustrated here:

![multi-view](https://user-images.githubusercontent.com/8792647/173841115-084c6396-3843-4d9b-9951-f93c932100c3.png)

Tested manually by triggering the above actions within multiple split graph windows and asserting that they are only applied to their corresponding graphs.

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Commit messages:
 - Apply toolbar actions to the graph window that is actually active

Changes: https://git.openjdk.org/jdk/pull/9169/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9169&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288480
  Stats: 8 lines in 1 file changed: 0 ins; 7 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9169.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9169/head:pull/9169

PR: https://git.openjdk.org/jdk/pull/9169