Follow-up to #12472 (and prior)

Change

• Use controller locking to prevent document refresh during writing.
  Drastically improves the performance of write operations in the document, making them appear almost instantaneous (earlier, there used to be a "flicker" effect, causing delay when inserting/updating citations/bibliography - which especially used to get increasingly worse as the number of citations increased).

Before:

After:

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.