Closes #13031

1. Introduce a new toggle button
2. Toggle button is synced with change in directory path and vice-versa
3. Tooltip displayed and also synchronous with change in specified directory (relative/absolute) and vice-versa
4. Toggle button is disabled for unsaved libraries
5. Directory is checked against relative path to library path and displayed relative (for saved libraries only)

Saved libraries:

Unsaved libraries:

Mandatory checks

• I own the copyright of the code submitted and I license 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 (if change is visible to the user)
• 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.