Merge bitcoin/bitcoin#32631: refactor: Convert GenTxid to std::variant

a60f863d3e scripted-diff: Replace GenTxidVariant with GenTxid (marcofleon)
c8ba199598 Remove old GenTxid class (marcofleon)
072a198ea4 Convert remaining instances of GenTxid to GenTxidVariant (marcofleon)
1b528391c7 Convert `txrequest` to GenTxidVariant (marcofleon)
bde4579b07 Convert `txdownloadman_impl` to GenTxidVariant (marcofleon)
c876a892ec Replace GenTxid with Txid/Wtxid overloads in `txmempool` (marcofleon)
de858ce2be move-only: make GetInfo a private CTxMemPool member (stickies-v)
eee473d9f3 Convert `CompareInvMempoolOrder` to GenTxidVariant (marcofleon)
243553d590 refactor: replace get_iter_from_wtxid with GetIter(const Wtxid&) (stickies-v)
fcf92fd640 refactor: make CTxMemPool::GetIter strongly typed (marcofleon)
11d28f21bb Implement GenTxid as a variant (marcofleon)

Pull request description:

  Part of the [type safety refactor](https://github.com/bitcoin/bitcoin/pull/32189).

  This PR changes the GenTxid class to a variant, which holds both Txids and Wtxids. This provides compile-time type safety and eliminates the manual type check (bool m_is_wtxid). Variables that can be either a Txid or a Wtxid are now using the new GenTxid variant, instead of uint256.

ACKs for top commit:
  w0xlt:
    ACK a60f863d3e
  dergoegge:
    Code review ACK a60f863d3e
  maflcko:
    review ACK a60f863d3e 🎽
  theStack:
    Code-review ACK a60f863d3e

Tree-SHA512: da9b73b7bdffee2eb9281a409205519ac330d3336094d17681896703fbca8099608782c9c85801e388e4d90af5af8abf1f34931f57bbbe6e9674d802d6066047

src/node/mempool_persist.cpp

@@ -107,7 +107,7 @@ bool LoadMempool(CTxMemPool& pool, const fs::path& load_path, Chainstate& active
                     // wallet(s) having loaded it while we were processing
                     // mempool transactions; consider these as valid, instead of
                     // failed, but mark them as 'already there'
-                    if (pool.exists(GenTxid::Txid(tx->GetHash()))) {
+                    if (pool.exists(tx->GetHash())) {
                         ++already_there;
                     } else {
                         ++failed;