Merge #16753: wallet: extract PubKey from P2PK script with Solver

798a589 wallet: extract PubKey from P2PK script with Solver (Sebastian Falbesoner)

Pull request description:

  The function `ExtractPubKey()` checks if a given script matches the P2PK pattern
  (`<PubKey> OP_CHECKSIG`), extracts the PubKey and additionally checks if it is
  cryptographically valid (full validation with ECC library via `CPubKey::IsFullyValid()`).

  Currently this is done manually in the following order:
  1. check if first script OP is data push with valid PubKey length (first part of pattern match), extract PubKey
  2. create `CPubKey` object with extracted PubKey
  3. fully validate public key
  4. check if last script OP is `OP_CHECKSIG` (second part of pattern match)

  Using Solver, the pattern matching and PubKey extraction can be done via a
  single step, leading to the following simplified order with shorter code:
  1. check if given script matches P2PK pattern with Solver (also contains valid PubKey length check), extracts Pubkey
  2. create `CPubKey` object with extracted Pubkey
  3. fully validate public key

ACKs for top commit:
  instagibbs:
    utACK bitcoin/bitcoin@798a589
  theStack:
    > utACK [798a589](bitcoin/bitcoin@798a589)
  sipa:
    ACK 798a589
  achow101:
    Code Review ACK 798a589

Tree-SHA512: 350358a89afed8c2a7967c50e9714a2d4a909259b50e694ce68dde3e7d0fa0bf3238d33642e73f2bdb53860f6d3f7327ca3eb6426b74eaffacfbca0a384d68cd

Author: fanquake

src/wallet/wallet.cpp

@@ -523,18 +523,9 @@ bool CWallet::LoadCScript(const CScript& redeemScript)
 
 static bool ExtractPubKey(const CScript &dest, CPubKey& pubKeyOut)
 {
-    //TODO: Use Solver to extract this?
-    CScript::const_iterator pc = dest.begin();
-    opcodetype opcode;
-    std::vector<unsigned char> vch;
-    if (!dest.GetOp(pc, opcode, vch) || !CPubKey::ValidSize(vch))
-        return false;
-    pubKeyOut = CPubKey(vch);
-    if (!pubKeyOut.IsFullyValid())
-        return false;
-    if (!dest.GetOp(pc, opcode, vch) || opcode != OP_CHECKSIG || dest.GetOp(pc, opcode, vch))
-        return false;
-    return true;
+    std::vector<std::vector<unsigned char>> solutions;
+    return Solver(dest, solutions) == TX_PUBKEY &&
+        (pubKeyOut = CPubKey(solutions[0])).IsFullyValid();
 }
 
 bool CWallet::AddWatchOnlyInMem(const CScript &dest)