Resolve long comments overflowing the container on MR Diffs when unified diff components is enabled

What does this MR do?

Solves a bug with the grids layout of diffs where overflowing context would extend far beyond the container's width.

The reason for why this fix works is described in this article: https://css-tricks.com/preventing-a-grid-blowout/

This MR tries to replace the existing proposed solution in !50715 (merged)

Screenshots (strongly suggested)

Before	After

Covers:

• draft comments - inline
• draft comments - parallel
• published comments - inline
• published comments - parallel

Does this MR meet the acceptance criteria?

Conformity

• (not needed, behind FF) Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #296222 (closed)