Add a title guess method to get "better" title

[leaf-soba]

• Closes:#11999
• As the issue said I should "traditional" (non-AI) code, so I write a AI-liked code in a simple traditional way. Since I don't have enough data, so the rules is limited now.
• I didn't add it PdfMergeMetadataImporterTest now, since I'm not sure if we like this kind of method or not, so I want to set up the PR with a demo code to discuss it first. I'll add it to PdfMergeMetadataImporter with a better clear code if we like it.

Mandatory checks

• [x] 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 applicable)
• [x] Tests created for changes (if applicable)
• [x] 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.