[llvm] [ADT] Introduce a `static_cast_to` (PR #165803)

[Yanzuo Liu via llvm-commits]

================
@@ -1704,6 +1704,11 @@ auto sum_of(R &&Range, E Init = E{0}) {
   return accumulate(std::forward<R>(Range), std::move(Init));
 }
 
+/// Return a range where each value of `R` is static_cast to `T`
+template <typename T, typename R> auto static_cast_to(R &&Range) {
+  return map_range(Range, [](const auto &V) { return static_cast<T>(V); });
----------------
zwuis wrote:

```cpp
[](auto &V) -> decltype(auto) { return static_cast<T>(V); }
```

Perheps `-> decltype(auto)` is needed to allow returning reference.

https://github.com/llvm/llvm-project/pull/165803