Prepare security widget for GraphQL migration

What does this MR do and why?

This MR does not introduce any UI/UX changes. It is simply a refactor to prepare it for the GraphQL migration implementation > MR Security widget - migrate to GraphQL (&10962)

fetchCollapsedData() {
-  // COPIED: REST implementation... 
+  this.fetchCollapsedDataREST()
}

+ fetchCollapsedDataREST() {
+    // PASTED: extracted REST implementation
+ }

References

Screenshots or screen recordings

Before (same)	After (same)
	same as before
Modal opens	same as before

How to set up and validate locally

1. No visual changes, this is simply a code change

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #574439