Fix: #12274 Import at "Find Unlinked Files" should not re-add an identical entry

[rocket125]

Closes #12274

Summary

This fix prevents "Search for unlinked local files" from re-adding already imported files with a second click on "Import". All import files will be unchecked. This provides visual indication to the user that their import is finish.

Changes Made

• startImport in UnlinkedFilesDialog unchecks all files after importing

Mandatory checks

• I own the copyright of the code submitted and I licence it under the MIT license
• Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[github-actions]

Your code currently does not meet JabRef's code guidelines.
We use OpenRewrite to ensure "modern" Java coding practices.
The issues found can be automatically fixed.
Please execute the gradle task rewriteRun, check the results, commit, and push.

You can check the detailed error output by navigating to your pull request, selecting the tab "Checks", section "Tests" (on the left), subsection "OpenRewrite".

[koppor]

I think, our issue description was not precise.

We added a test scenrio (at #12507) and a refined issue desription at #12274 (comment)

Please rewrite your code accordingly.

[rocket125]

I read the updated issue description

Disable combobox for imported files. --> This will indicate for the users that the file was imported

How would I proceed in disabling the comboboxes? I can only uncheck them.

[github-actions]

Your code currently does not meet JabRef's code guidelines.
We use Checkstyle to identify issues.
Please carefully follow the setup guide for the codestyle.
Afterwards, please run checkstyle locally and fix the issues.

In case of issues with the import order, double check that you activated Auto Import.
You can trigger fixing imports by pressing Ctrl+Alt+O to trigger Optimize Imports.

[koppor]

I read the updated issue description

Disable combobox for imported files. --> This will indicate for the users that the file was imported

How would I proceed in disabling the comboboxes? I can only uncheck them.

Uncheck is OK.

Disabling is blocked by controlsfx/controlsfx#825.