Move Hashers to util/hasher.{cpp/h}

Move the hashers that we use for hash tables to a common place.

Moved hashers:
- SaltedTxidHasher
- SaltedOutpointHasher
- FilterHeaderHasher
- SignatureCacheHasher
- BlockHasher

src/script/sigcache.h

@@ -8,6 +8,7 @@
 
 #include <script/interpreter.h>
 #include <span.h>
+#include <util/hasher.h>
 
 #include <vector>
 
@@ -20,27 +21,6 @@ static const int64_t MAX_MAX_SIG_CACHE_SIZE = 16384;
 
 class CPubKey;
 
-/**
- * We're hashing a nonce into the entries themselves, so we don't need extra
- * blinding in the set hash computation.
- *
- * This may exhibit platform endian dependent behavior but because these are
- * nonced hashes (random) and this state is only ever used locally it is safe.
- * All that matters is local consistency.
- */
-class SignatureCacheHasher
-{
-public:
-    template <uint8_t hash_select>
-    uint32_t operator()(const uint256& key) const
-    {
-        static_assert(hash_select <8, "SignatureCacheHasher only has 8 hashes available.");
-        uint32_t u;
-        std::memcpy(&u, key.begin()+4*hash_select, 4);
-        return u;
-    }
-};
-
 class CachingTransactionSignatureChecker : public TransactionSignatureChecker
 {
 private: