message: Implement IsMine for DescriptorScriptPubKeyMan
  Adds a set of scriptPubKeys that DescriptorScriptPubKeyMan tracks.
  If the given script is in that set, it is considered ISMINE_SPENDABLE
diff: @@ -1502,6 +1502,10 @@ bool DescriptorScriptPubKeyMan::GetNewDestination(const OutputType type, CTxDest
  isminetype DescriptorScriptPubKeyMan::IsMine(const CScript& script) const
  {
  + LOCK(cs_desc_man);
  + if (m_map_script_pub_keys.count(script) > 0) {
  + return ISMINE_SPENDABLE;
  + }
  return ISMINE_NO;
  }
  @@ -1575,7 +1579,7 @@ std::unique_ptr<SigningProvider> DescriptorScriptPubKeyMan::GetSolvingProvider(c
  bool DescriptorScriptPubKeyMan::CanProvide(const CScript& script, SignatureData& sigdata)
  {
  - return false;
  + return IsMine(script);
  }
  bool DescriptorScriptPubKeyMan::SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, std::string>& input_errors) const
  