[clang] [LifetimeSafety] Use ImmutableList for buildOriginFlowChain DFS nodes (PR #208890)

[Utkarsh Saxena via cfe-commits]

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@@ -86,6 +86,7 @@ void LifetimeSafetyAnalysis::run() {
   ///    the analysis.
   /// 3. Collapse ExpireFacts belonging to same source location into a single
   ///    Fact.
+
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usx95 wrote:

nit: revert unintentional change.

https://github.com/llvm/llvm-project/pull/208890