Merge bitcoin/bitcoin#28687: C++20 std::views::reverse

2925bd537c refactor: use c++20 std::views::reverse instead of reverse_iterator.h (stickies-v)

Pull request description:

  C++20 introduces [`std::ranges::views::reverse`](https://en.cppreference.com/w/cpp/ranges/reverse_view), which allows us to drop our own `reverse_iterator.h` implementation and also makes it easier to chain views (even though I think we currently don't use this).

ACKs for top commit:
  achow101:
    ACK 2925bd537c
  maflcko:
    ACK 2925bd537c 🎷

Tree-SHA512: 567666ec44af5d1beb7a271836bcc89c4c577abc77f522fcc18bc6d4de516ae9b0df766d0bfa6dd217569e6878331c2aee1d9815620860375e3510dad7fed476

src/node/blockstorage.cpp

@@ -20,7 +20,6 @@
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <random.h>
-#include <reverse_iterator.h>
 #include <serialize.h>
 #include <signet.h>
 #include <span.h>
@@ -38,6 +37,7 @@
 #include <validation.h>
 
 #include <map>
+#include <ranges>
 #include <unordered_map>
 
 namespace kernel {
@@ -579,7 +579,7 @@ const CBlockIndex* BlockManager::GetLastCheckpoint(const CCheckpointData& data)
 {
     const MapCheckpoints& checkpoints = data.mapCheckpoints;
 
-    for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints)) {
+    for (const MapCheckpoints::value_type& i : checkpoints | std::views::reverse) {
         const uint256& hash = i.second;
         const CBlockIndex* pindex = LookupBlockIndex(hash);
         if (pindex) {