TINYDOC-3562 - Document beforeSetContent listener for AI-only revision history

[kemister85]

Ticket: TINYDOC-3562

Site: Staging branch

Changes:

• Add a "Capturing content before and after an AI edit" subsection to the "Saving an AI-assisted revision" section of revisionhistory.adoc.
• Document listening for the BeforeSetContent event and checking e.ai to capture the latest non-AI (human) content via editor.getContent() and store it as a revision before the AI-generated content is inserted.
• Pair the new BeforeSetContent example with the existing SetContent example so integrators can save a clean pre-AI revision alongside the post-AI, AI-assisted revision for finer-grained history.
• Clarify that listening for BeforeSetContent is optional — integrators can use SetContent alone or pair both events, depending on their use case.

Pre-checks:

• Branch is correctly prefixed: hotfix/8/TINYDOC-3562
• Files have been included where required (if applicable).
• Build passes without console errors, warnings, or issues.

Prepared for documentation team review.