Clean up banning levels

Compared with previous bans, the following changes are made:
 * Txn with empty vin/vout or null prevouts move from 10 DoS
   points to 100.
 * Loose transactions with a dependency loop now result in a ban
   instead of 10 DoS points.
 * Many pre-segwit soft-fork errors now result in a ban.
   Note: Transactions that violate soft-fork script flags since P2SH do not generally
   result in a ban. Also, banning behavior for invalid blocks is dependent on
   whether the node is validating with multiple script check threads, due to a long-
   standing bug. That inconsistency is still present after this commit.
 * Proof of work failure moves from 50 DoS points to a ban.
 * Blocks with timestamps under MTP now result in a ban, blocks
   too far in the future continue to *not* result in a ban.
 * Inclusion of non-final transactions in a block now results in a
   ban instead of 10 DoS points.

Co-authored-by: Anthony Towns <aj@erisian.com.au>

src/consensus/tx_verify.cpp

@@ -172,8 +172,8 @@ bool Consensus::CheckTxInputs(const CTransaction& tx, CValidationState& state, c
 
         // If prev is coinbase, check that it's matured
         if (coin.IsCoinBase() && nSpendHeight - coin.nHeight < COINBASE_MATURITY) {
-            return state.Invalid(false,
-                REJECT_INVALID, "bad-txns-premature-spend-of-coinbase",
+            return state.DoS(0, false,
+                REJECT_INVALID, "bad-txns-premature-spend-of-coinbase", false,
                 strprintf("tried to spend coinbase at depth %d", nSpendHeight - coin.nHeight));
         }