RFR: JDK-8290016: IGV: Fix graph panning when mouse dragged outside of window

[Tobias Holenstein]

A graph in IGV can be moved by dragging it with the left mouse button (called panning). 
![panning](https://user-images.githubusercontent.com/71546117/178509416-24dd900f-131b-484b-af47-c7a78e791434.png)

If the mouse left the visible window of the graph during dragging, the diagram started to move in the opposite direction. This was annoying. Now panning stops as soon as the mouse leaves the window. 
![stop reverse panning](https://user-images.githubusercontent.com/71546117/178509309-3df03b7a-ada4-45a3-b9a7-d6e10664033d.png)

In selection mode, the graph still moves when the mouse is dragged outside the window, as this is meant to make a larger selection. 
![keep panning for selection](https://user-images.githubusercontent.com/71546117/178509302-74fa41d2-e611-40a3-b6b0-c937ef4b2462.png)

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Commit messages:
 - remove imports
 - JDK-8290016: IGV: Fix graph panning when mouse dragged outside of window

Changes: https://git.openjdk.org/jdk/pull/9470/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9470&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290016
  Stats: 77 lines in 2 files changed: 23 ins; 20 del; 34 mod
  Patch: https://git.openjdk.org/jdk/pull/9470.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9470/head:pull/9470

PR: https://git.openjdk.org/jdk/pull/9470