Added markdown in AI chat

[ar-rana]

Closes #12234

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.

[github-actions]

JUnit tests are failing. In the area "Some checks were not successful", locate "Tests / Unit tests (pull_request)" and click on "Details". This brings you to the test output.

You can then run these tests in IntelliJ to reproduce the failing tests locally. We offer a quick test running howto in the section Final build system checks in our setup guide.

[calixtus]

Why do you replace the ExpandingTextArea?
Why don't you use our internal clipboard tools?