• Pre-condition for Fix 11102 by allowing users to add local bst files to preview layout list #11234
• Folow-up to Update BST VM to Antlr4 #8934

Seperate PR to focus on the VM and not to "pollute" the student PR. (And I had write issues to the branch there)

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• 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.