Merge #21366: refactor: replace util::Ref with std::any (C++17)

916ab0195d remove unused class util::Ref and its unit test (Sebastian Falbesoner)
8dbb87a393 refactor: replace util::Ref by std::any (C++17) (Sebastian Falbesoner)
95cccf8a4b util: introduce helper AnyPtr to access std::any instances (Sebastian Falbesoner)

Pull request description:

  As described in `util/ref.h`: "_This implements a small subset of the functionality in C++17's std::any class, and **can be dropped when the project updates to C++17**_". For accessing the contained object of a `std::any` instance, a helper template function `AnyPtr` is introduced (thanks to ryanofsky).

ACKs for top commit:
  hebasto:
    re-ACK 916ab0195d, with command
  ryanofsky:
    Code review ACK 916ab0195d. Changes since last review: rebase and replacing types with `auto`. I might have used `const auto*` and `auto*` instead of plain `auto` because I think the qualifiers are useful, but this is all good.

Tree-SHA512: fe2c3e4f5726f8ad40c61128339bb24ad11d2c261f71f7b934b1efe3e3279df14046452b0d9b566917ef61d5c7e0fd96ccbf35ff810357e305710f5002c27d47

src/node/interfaces.cpp

@@ -38,7 +38,6 @@
 #include <uint256.h>
 #include <univalue.h>
 #include <util/check.h>
-#include <util/ref.h>
 #include <util/system.h>
 #include <util/translation.h>
 #include <validation.h>
@@ -49,6 +48,7 @@
 #include <config/bitcoin-config.h>
 #endif
 
+#include <any>
 #include <memory>
 #include <optional>
 #include <utility>
@@ -298,13 +298,13 @@ public:
     {
         m_context = context;
         if (context) {
-            m_context_ref.Set(*context);
+            m_context_ref = context;
         } else {
-            m_context_ref.Clear();
+            m_context_ref.reset();
         }
     }
     NodeContext* m_context{nullptr};
-    util::Ref m_context_ref;
+    std::any m_context_ref;
 };
 
 bool FillBlock(const CBlockIndex* index, const FoundBlock& block, UniqueLock<RecursiveMutex>& lock, const CChain& active)