[merge editor] Improve scroll sync implementation

[pisv]

What it does

Fixes #16946.

How to test

Use the reproduction steps in #16946 to verify that the issue is fixed.

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines
• User-facing text is internationalized using the nls service (for details, please see the Internationalization/Localization section in the Coding Guidelines)

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[ndoschek]

Thanks again for your improvement for the merge editor @pisv!
Scrolling is now perfectly in sync 😄

[pisv]

Great to hear that 😄 Thanks a lot for your review @ndoschek!