[clang] [llvm] [mlir] [ADT] Give DenseMapPair its own members instead of a std::pair base. NFC (PR #221853)

[Kazu Hirata via llvm-commits]

================
@@ -732,7 +732,8 @@ static bool findArgParts(Argument *Arg, const DataLayout &DL, AAResults &AAR,
     return true; // No users, this is a dead argument.
 
   // Sort parts by offset.
-  append_range(ArgPartsVec, ArgParts);
+  for (const auto &Part : ArgParts)
+    ArgPartsVec.emplace_back(Part.first, Part.second);
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kazutakahirata wrote:

Could we use structured bindings here?

```cpp
for (const auto &[Offset, Part] : ArgParts)
  ArgPartsVec.emplace_back(Offset, Part);
```


https://github.com/llvm/llvm-project/pull/221853