[llvm] [ADT] Add DenseSet::insert_range (PR #131567)

[Kazu Hirata via llvm-commits]

================
@@ -237,6 +238,10 @@ class DenseSetImpl {
     for (; I != E; ++I)
       insert(*I);
   }
+
+  template <typename Range> void insert_range(Range &&R) {
+    insert(adl_begin(R), adl_end(R));
----------------
kazutakahirata wrote:

Ah, I see.  Thanks!  In that particular case, is `insert_range` worse than `insert`?  I think we'd still end with something like:

```
auto R = std::move(foo);
set.insert(adl_begin(R), adl_end(R));
```


https://github.com/llvm/llvm-project/pull/131567