refactor org.jabref.gui.journals.UndoableAbbreviator#abbreviate

[tina9452]

I refactored org.jabref.gui.journals.UndoableAbbreviator#abbreviate. This is the first step for issue #11791

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.

[koppor]

Do not remove comments adding value

[github-actions]

Your code currently does not meet JabRef's code guidelines.
We use Checkstyle to identify issues.
The tool reviewdog already placed comments on GitHub to indicate the places. See the tab "Files" in you PR.
Please carefully follow the setup guide for the codestyle.
Afterwards, please run checkstyle locally and fix the issues.

You can check review dog's comments at the tab "Files changed" of your pull request.

[koppor]

Closing this issue due to inactivity 💤

Please ping us if you intend to resume work on this one.