[validation] add TxValidationResult::TX_RECONSIDERABLE, TX_UNKNOWN

With package validation rules, transactions that fail individually may
sometimes be eligible for reconsideration if submitted as part of a
(different) package. For now, that includes trasactions that failed for
being too low feerate.  Add a new TxValidationResult type to distinguish
these failures from others.  In the next commits, we will abort package
validation if a tx fails for any other reason. In the future, we will
also decide whether to cache failures in recent_rejects based on this
result (we won't want to reject a package containing a transaction that
was rejected previously for being low feerate).

Package validation also sometimes elects to skip some transactions when
it knows the package will not be submitted in order to quit sooner. Add
a result to specify this situation; we also don't want to cache these
as rejections.

src/net_processing.cpp

@@ -1820,6 +1820,8 @@ bool PeerManagerImpl::MaybePunishNodeForTx(NodeId nodeid, const TxValidationStat
     case TxValidationResult::TX_CONFLICT:
     case TxValidationResult::TX_MEMPOOL_POLICY:
     case TxValidationResult::TX_NO_MEMPOOL:
+    case TxValidationResult::TX_RECONSIDERABLE:
+    case TxValidationResult::TX_UNKNOWN:
         break;
     }
     return false;