Merge #21415: refactor: remove Optional & nullopt

ebc4ab721b refactor: post Optional<> removal cleanups (fanquake)
57e980d13c scripted-diff: remove Optional & nullopt (fanquake)

Pull request description:

  Same rationale & motivation as #21404, which turned out to be quite low in the number of potential conflicts. Lets see what the bot has to say here.

ACKs for top commit:
  practicalswift:
    cr ACK ebc4ab721b: patch looks correct
  jnewbery:
    utACK ebc4ab721b
  laanwj:
    Code review ACK ebc4ab721b

Tree-SHA512: 550fbeef09b9d35ddefaa805d1755c18c8fd499c4b0f77ebfece8c20296a7abd1cf6c699e2261f92fe3552deeb7555ec2a2287ffe3ab9e98bb9f8612a4d43be3

src/validation.h

@@ -17,7 +17,6 @@
 #include <crypto/common.h> // for ReadLE64
 #include <fs.h>
 #include <node/utxo_snapshot.h>
-#include <optional.h>
 #include <policy/feerate.h>
 #include <protocol.h> // For CMessageHeader::MessageStartChars
 #include <script/script_error.h>
@@ -32,6 +31,7 @@
 #include <atomic>
 #include <map>
 #include <memory>
+#include <optional>
 #include <set>
 #include <stdint.h>
 #include <string>
@@ -205,8 +205,7 @@ struct MempoolAcceptResult {
 
     /** Constructor for failure case */
     explicit MempoolAcceptResult(TxValidationState state)
-        : m_result_type(ResultType::INVALID),
-        m_state(state), m_replaced_transactions(nullopt), m_base_fees(nullopt) {
+        : m_result_type(ResultType::INVALID), m_state(state) {
             Assume(!state.IsValid()); // Can be invalid or error
         }
 
@@ -924,7 +923,7 @@ public:
 
     bool IsSnapshotActive() const;
 
-    Optional<uint256> SnapshotBlockhash() const;
+    std::optional<uint256> SnapshotBlockhash() const;
 
     //! Is there a snapshot in use and has it been fully validated?
     bool IsSnapshotValidated() const { return m_snapshot_validated; }