Merge #19935: Move SaltedHashers to separate file and add some new ones

281fd1a4a0 Replace KeyIDHasher with SaltedSipHasher (Andrew Chow)
210b693db6 Add generic SaltedSipHasher (Andrew Chow)
95e61c1cf2 Move Hashers to util/hasher.{cpp/h} (Andrew Chow)

Pull request description:

  There are existing `SaltedOutPointHasher` and `SaltedTxidHasher` classes used for `std::unordered_map` and `std::unordered_set` that could be useful in other places in the codebase. So we these to their own `saltedhash.{cpp/h}` file. An existing `KeyIDHasher` is moved there too. Additionally, `ScriptIDHasher`, `SaltedPubkeyHasher`, and `SaltedScriptHasher` are added so that they can be used in future work.

  `KeyIDHasher` and `ScriptIDHasher` are not salted so that equality comparisons of maps and sets keyed by `CKeyID` and `CScriptID` will actually work.

  Split from #19602 (and a few other PRs/branches I have).

ACKs for top commit:
  laanwj:
    Code review ACK 281fd1a4a0
  jonatack:
    ACK 281fd1a4a0, code review, debug build and ran bitcoind after rebasing to master @ dff0f6f753
  fjahr:
    utACK 281fd1a4a0

Tree-SHA512: bb03b231ccf3c9ecefc997b8da9c3770af4819f9be5b0a72997a103864e84046a2ac39b8eadf0dc9247bdccd53f86f433642e3a098882e6748341a9e7736271b

src/validation.h

@@ -23,6 +23,7 @@
 #include <txdb.h>
 #include <versionbits.h>
 #include <serialize.h>
+#include <util/hasher.h>
 
 #include <atomic>
 #include <map>
@@ -93,14 +94,6 @@ static const unsigned int DEFAULT_CHECKLEVEL = 3;
 // Setting the target to >= 550 MiB will make it likely we can respect the target.
 static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
 
-struct BlockHasher
-{
-    // this used to call `GetCheapHash()` in uint256, which was later moved; the
-    // cheap hash function simply calls ReadLE64() however, so the end result is
-    // identical
-    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
-};
-
 /** Current sync state passed to tip changed callbacks. */
 enum class SynchronizationState {
     INIT_REINDEX,