RFR: 8263384: IGV: Outline should highlight the Graph that has focus

[Roberto Castañeda Lozano]

This changeset eases navigation within and across graph groups by highlighting the focused graph in the Outline window. If the user changes the focus to another graph window, or moves to the previous or next graph within the same window, the newly focused graph is automatically highlighted in the Outline window. This is implemented by maintaining a static map from opened graphs to their corresponding [NetBeans nodes](https://netbeans.apache.org/tutorials/nbm-selection-2.html). The Outline window uses the map to select, on a graph focus change, the NetBeans node of the newly focused graph that should be highlighted.

Tested manually by opening simultaneously tens of graphs from different groups and switching the focus randomly.

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Commit messages:
 - Highlight focused graph in outline

Changes: https://git.openjdk.org/jdk/pull/9167/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9167&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8263384
  Stats: 56 lines in 2 files changed: 50 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/9167.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9167/head:pull/9167

PR: https://git.openjdk.org/jdk/pull/9167