RFR: 8345041: IGV: Free Placement Mode in IGV Layout

[Tobias Holenstein]

This PR depends on https://github.com/openjdk/jdk/pull/22430. To check out this PR locally: 

git fetch https://git.openjdk.org/jdk.git pull/22438/head:pull/22438
git checkout pull/22438


Introduce a Free Placement Mode to IGV, allowing users to position nodes freely without being limited to the hierarchical layout constraints.

In this mode, users can manually drag and place nodes anywhere within the space, giving them complete control over the visual arrangement of the graph. Connections between nodes will be rendered as straight (or S curved) lines, without recalculating or enforcing hierarchical constraints.

This feature is ideal for users who need a flexible, non-restrictive way to organize and visualize complex graph structures in a customized and intuitive manner. The free placement of nodes will remain persistent until the layout is reset or another layout mode is selected.

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Depends on: https://git.openjdk.org/jdk/pull/22430

Commit messages:
 - JDK-8345041 IGV: Free Placement Mode in IGV Layout

Changes: https://git.openjdk.org/jdk/pull/22438/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22438&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345041
  Stats: 612 lines in 11 files changed: 592 ins; 0 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/22438.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22438/head:pull/22438

PR: https://git.openjdk.org/jdk/pull/22438