[Security Solution] Update flyout diff view for "My changes merged with Elastic's" changes

[approksiu]

Describe the bug:

When a user switches between the diff comparisons on the customized field that has update, the "My changes merged with Elastic's" diff changes to the same as "Update from Elastic". It looks like the proper versions are back when the page refresh happens.

Kibana/Elasticsearch Stack version:

VERSION: 9.0.0

Functional Area (e.g. Endpoint management, timelines, resolver, etc.):

Rule Update

Pre requisites:

1. prebuiltRulesCustomizationEnabled flag is enabled
2. Prebuilt rules are available
3. At least one prebuilt rule has an update with updated field modified.

Steps to reproduce:

1. Locate a prebuilt rule that has an available update to a modified field.
2. Switch between different diffs in the left side of the flyout.

Current behavior:

When opening the "My changes merged with Elastic's" after viewing other diffs, the value in the diff changes and does not contain both "My" and Elastic's changes.

Expected behavior:
"My changes merged with Elastic's" stays the same (correct) when coming back to it after switching between different diff options.

Screenshots:

Diff_flyout_Screen.Recording.2025-01-23.at.16.24.43.mov

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-detection-rule-management (Team:Detection Rule Management)

[elasticmachine]

Pinging @elastic/security-detections-response (Team:Detections and Resp)

[banderror]

@approksiu Oh yeah, I noticed this one too a while ago and wanted to open a ticket. Thank you!