Enable resetting of NameDisplayPreferences

[jatinkumarsingh]

Closes #14412

This PR enables resetting for NameDisplayPreferences according to the requirements in the parent issue.
A private default constructor was added with all default values, along with getDefault() and setAll(). The loading and clearing logic in JabRefGuiPreferences has been updated so that NameDisplayPreferences can now be reset independently via the preferences reset/import system.

Steps to test

Open Options → Preferences → Entry table / Name display.

Change any setting related to NameDisplayPreferences (e.g., name formatting options).

Use Reset preferences or Import settings.

Verify that:

All NameDisplayPreferences values return to their defaults.

Restarting JabRef preserves the reset state.

Exporting/importing settings includes this preference and restores it correctly.

Mandatory checks

I own the copyright of the code submitted and I license it under the MIT license

I manually tested my changes in running JabRef (always required)

I added JUnit tests for changes (if applicable)

I added screenshots in the PR description (if change is visible to the user)

I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)

I checked the user documentation; if updates were needed, I opened an issue or PR in the user-docs repository

[github-actions]

Hey @jatinkumarsingh!

Thank you for contributing to JabRef! Your help is truly appreciated ❤️

We have automated checks in place, based on which you will soon get feedback if any of them are failing. In a while, maintainers will also review your contribution. Once that happens, you can go through their comments in the "Files changed" tab and act on them, or reply to the conversation if you have further inputs.

Please re-check our contribution guide in case of any other doubts related to our contribution workflow.

[jabref-machine]

Note that your PR will not be reviewed/accepted until you have gone through the mandatory checks in the description and marked each of them them exactly in the format of [x] (done), [ ] (not done yet) or [/] (not applicable).

[jabref-machine]

You have removed the "Mandatory Checks" section from your pull request description. Please adhere to our pull request template.

[jabref-machine]

While the PR was in progress, a new version of JabRef has been released.

You have to merge upstream/main and move your entry in CHANGELOG.md up to the section ## [Unreleased].

[calixtus]

This is weird.