[llvm] [ADT] Add computeNumBuckets to DenseMap (NFC) (PR #168301)

[Sergei Barannikov via llvm-commits]

================
@@ -1106,10 +1112,14 @@ class SmallDenseMap
     new (getLargeRep()) LargeRep{nullptr, 0};
   }
 
-  void grow(unsigned AtLeast) {
-    if (AtLeast > InlineBuckets)
-      AtLeast = std::max<unsigned>(64, NextPowerOf2(AtLeast - 1));
+  static unsigned computeNumBuckets(unsigned NumBuckets) {
+    if (NumBuckets > InlineBuckets)
+      NumBuckets =
+          std::max(64u, static_cast<unsigned>(NextPowerOf2(NumBuckets - 1)));
+    return NumBuckets;
+  }
 
+  void grow(unsigned AtLeast) {
----------------
s-barannikov wrote:

```suggestion
  void grow(unsigned NumBuckets) {
```
Same in the non-small case.

https://github.com/llvm/llvm-project/pull/168301