[OO] Major performance improvements & fixes

[subhramit]

CSL4LibreOffice - Performance improvements and fixes

Closes https://github.com/JabRef/jabref-issue-melting-pot/issues/697

• Reduces the number of UNO API calls -
  a) The OOTextIntoOO#write() method by default shifts the cursor to the end of the text after operations are done, so calling cursor.collapseToEnd() everywhere is needless.
  b) Explicit deletion of extra newlines/paragraph breaks using cursor.setString() is no longer needed in case of numeric styles - RegEx in transformHTML is now adapted to handle it before it is inserted into the document, which is way faster.

• Changes newlines in bibliography to paragraph breaks, improving performance of documents with a large number of bibliographic entries drastically, as per information from https://bugs.documentfoundation.org/show_bug.cgi?id=163984
  Old:
  
  New:
  

• Fixes extra newlines before each numeric bibliographic entry, which also used to cause one to be placed after the title (see comparison above)

• Some miscellaneous documentation enhancements

Credits to @ThiloteE for investigating and the @LibreOffice community for prompt support!

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) [Changes in unreleased]
• 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.

[subhramit]

Feels weird to not pass my own tests 😅
Thankfully for good reason. We don't need the unnecessary newlines anymore.

[calixtus]

Looks good. Thanks for keeping up the work on your code.