Fix content not correctly parsed at pdf content importer

[leaf-soba]

Closes #12278

1. is far away should compare with the last one in font size, not the former text
2. fix the abs value issue.
3. fix the Ygap calculate issue.

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.

[Siedlerchr]

@InAnYan You are currently more into the pdf parsing, can you take a look?

[Siedlerchr]

Tests are inlcuded so from my point of view this is fine

[Siedlerchr]

As we released 6.0 alpha, can you please add a changelog entry like?
We improved the offline pdf content parsing