[llvm] [ADT] Refactor MapVector::insert, try_emplace, and operator[] (NFC) (PR #155205)

[Jakub Kuderski via llvm-commits]

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@@ -51,6 +44,28 @@ class MapVector {
   using reverse_iterator = typename VectorType::reverse_iterator;
   using const_reverse_iterator = typename VectorType::const_reverse_iterator;
 
+private:
+  MapType Map;
+  VectorType Vector;
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kuhar wrote:

Maybe move the private section to the end of the class?

https://github.com/llvm/llvm-project/pull/155205