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

[Baranov Victor via llvm-commits]

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@@ -379,6 +379,17 @@ TEST(DenseMapCustomTest, EqualityComparison) {
   EXPECT_NE(M1, M3);
 }
 
+TEST(DenseMapCustomTest, InsertRange) {
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vbvictor wrote:

Added `SmallDenseMap`, should I still leave test for `SmallDenseSet` because it was absent?

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