[clang] [clang][dataflow] Allow `DataflowAnalysisContext` to use a non-owned `Solver`. (PR #91316)

[Yitzhak Mandelbaum via cfe-commits]

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@@ -209,6 +221,9 @@ class DataflowAnalysisContext {
     using DenseMapInfo::isEqual;
   };
 
+  DataflowAnalysisContext(Solver &S, std::unique_ptr<Solver> OwnedSolver,
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ymand wrote:

Please add comments either here or on the fields relating S and OwnedSolver.

https://github.com/llvm/llvm-project/pull/91316