RFR: JDK-8291823: IGV: Fix "Save selected groups" [v3]

[Tobias Holenstein]

> In IGV the button `Save selected groups to XML file...` is broken and never activated. 
> 
> *Before this fix* 
> Bellow you can see the Outline with two selected groups, but the `Save selected groups to XML file...` button does not work:
> <img width="307" alt="before_groups_selected" src="https://user-images.githubusercontent.com/71546117/182790122-ed272ed4-1cca-4d5c-ae2a-6c2f44fd3565.png">
> 
> *After this fix* 
> Now the `Save selected groups to XML file...` button works if at least one groups is selected:
> <img width="273" alt="groups_selected" src="https://user-images.githubusercontent.com/71546117/182790406-08d6366a-4351-49d4-959e-79948bc4984d.png">
> 
> 
> *After this fix* 
> The `Save selected groups to XML file...` button is greyed out if no groups are selected:
> <img width="272" alt="no_groups_selected" src="https://user-images.githubusercontent.com/71546117/182792546-ef5169a8-d4d8-4981-aee1-af7e30895925.png">
> 
> 
> 
> 
> *Before this fix* 
> The `Save all groups to XML` and the `Remove all graphs and groups` buttons where available even if no graphs or groups were loaded:
> <img width="306" alt="before_no_groups" src="https://user-images.githubusercontent.com/71546117/182791984-dbec8829-fd81-4ce8-aa05-2d2030f89bd3.png">
> 
> *After this fix* 
> The `Save all groups to XML` and the `Remove all graphs and groups` buttons are greyed out if no graphs or groups are loaded:
> <img width="271" alt="no_groups" src="https://user-images.githubusercontent.com/71546117/182792159-88b0fa32-89dd-4e02-a3a9-66bdc77ecf70.png">

Tobias Holenstein has updated the pull request incrementally with one additional commit since the last revision:

  Deactivate RemoveAction and SaveAction if only (invisible) root folder is selected

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9730/files
  - new: https://git.openjdk.org/jdk/pull/9730/files/c838c082..930eea8b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9730&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9730&range=01-02

  Stats: 17 lines in 3 files changed: 14 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/9730.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9730/head:pull/9730

PR: https://git.openjdk.org/jdk/pull/9730