RFR: JDK-8324950: IGV: save the state to a file

[Tobias Holenstein]

The current workflow in IGV is the following:
1) import an XML file with graphs or send via network
2) open or more graphs in a tab
3) extract a set of nodes to be displayed in the tab
4) close IGV and start from 1) again

The idea of this RFE is to save the important **states** of IGV to a workspace directory:
- imported graphs (_graphs.xml_)
- opened graph tabs + extracted nodes (_state.igv_)


### Saving the state of IGV
- For IGV to save the state it needs a workspace, which can be passed in 3 different ways: 
  1) Using a global variable : `IGV_WORKSPACE=path/to/igv_workspace ./igv.sh`
  2) Passed as an argument : `./igv.sh path/to/igv_workspace `
  3) With default location `IdealGraphVisualizer/workspace` : `./igv.sh`

Open IGV with the following example workspace (unzipped) [igv_workspace.zip](https://github.com/openjdk/jdk/files/14311092/igv_workspace.zip) should look something like this:
![workspace](https://github.com/openjdk/jdk/assets/71546117/58da409d-fb02-4b21-8914-1cae9752b17f)


### Workspace
A workspace is a directory where IGV saves imported graphs  as _graphs.xml_ and  opened graph tabs to _state.igv_. A workspace is loaded when IGV is opened. The current workspace is saved when IGV is closed or when the workspace is changed to a different directory. When changing a directory the state of the new workspace is loaded.
- Click here to select a different workspace directory
![path](https://github.com/openjdk/jdk/assets/71546117/cff50c4d-fbc1-4112-916d-00f9ce14b27d)

- Imports an XML file (group and graphs) into the current workspace
![import XML](https://github.com/openjdk/jdk/assets/71546117/a92ae702-e599-4459-960d-849365dbaa1d)

- saves the state of the current workspace 
![save_workspace](https://github.com/openjdk/jdk/assets/71546117/16759da6-367b-47ce-997b-f176b0cbfc0f)
   - imported graphs (_graphs.xml_)
   - opened graph tabs + extracted nodes (_state.igv_)


- Export the selected groups to a separate XML file
![save_selected](https://github.com/openjdk/jdk/assets/71546117/20cc347c-7ff5-4181-8539-4ed585d5a0bc)

- Delete the selected groups and graphs
![delete_selected](https://github.com/openjdk/jdk/assets/71546117/1cb14b43-9b1a-4073-8964-075fc070a0b0)

- Clear the workspace and delete all groups and graphs
![clear_workspace](https://github.com/openjdk/jdk/assets/71546117/b40b1805-3f39-4d49-9bc2-0d538976cf25)



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### Progress
- [ ] Change must be properly reviewed (1 review required, with at least 1 [Reviewer](https://openjdk.org/bylaws#reviewer))
- [x] Change must not contain extraneous whitespace
- [x] Commit message must refer to an issue



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-------------

Commit messages:
 - USERDIR to WORKSPACE
 - invokeLater and correct getWorkspaceGraphsPath
 - clear() in loadWorkspace()
 - setWorkspacePath
 - import description
 - saveall.gif
 - temp
 - workspace button
 - missing saveas image
 - Compile again
 - ... and 8 more: https://git.openjdk.org/jdk/compare/bccd823c...96aba834

Changes: https://git.openjdk.org/jdk/pull/17630/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17630&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324950
  Stats: 516 lines in 28 files changed: 359 ins; 93 del; 64 mod
  Patch: https://git.openjdk.org/jdk/pull/17630.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17630/head:pull/17630

PR: https://git.openjdk.org/jdk/pull/17630