[llvm] [ADT] Move shrink_and_clear to DenseMapBase (NFC) (PR #165103)

[Jakub Kuderski via llvm-commits]

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@@ -861,6 +851,15 @@ class DenseMap : public DenseMapBase<DenseMap<KeyT, ValueT, KeyInfoT, BucketT>,
     deallocate_buffer(OldBuckets, sizeof(BucketT) * OldNumBuckets,
                       alignof(BucketT));
   }
+
+  std::pair<bool, unsigned> planShrinkAndClear() const {
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kuhar wrote:

Same comments as under the other function 

https://github.com/llvm/llvm-project/pull/165103