[llvm] [ADT] Add `DenseMap::insert_range` (PR #133600)

[Jakub Kuderski via llvm-commits]

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@@ -302,6 +303,10 @@ class DenseMapBase : public DebugEpochBase {
       insert(*I);
   }
 
+  template <typename Range> void insert_range(Range &&R) {
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kuhar wrote:

In this instance, I think it would be useful to add a comment explaining that `R` should be a range of key-value pairs to be inserted.

https://github.com/llvm/llvm-project/pull/133600