Merge bitcoin/bitcoin#26889: refactor: wallet, remove global 'ArgsManager' dependency

52f4d567d6 refactor: remove <util/system.h> include from wallet.h (furszy)
6c9b342c30 refactor: wallet, remove global 'ArgsManager' access (furszy)
d8f5fc4462 wallet: set '-walletnotify' script instead of access global args manager (furszy)
3477a28dd3 wallet: set keypool_size instead of access global args manager (furszy)

Pull request description:

  Structurally, the wallet class shouldn't access the global `ArgsManager` class, its internal behavior shouldn't be coupled to a global command line args parsing object.

  So this PR migrates the only two places where we depend on it: (1) the keypool size, and (2) the "-walletnotify" script. And cleans up the, now unneeded, wallet `ArgsManager` ref member.

  Extra note:
  In the process of removing the args ref member, discovered and fixed files that were invalidly depending on the wallet header including `util/system.h`.

ACKs for top commit:
  achow101:
    ACK 52f4d567d6
  TheCharlatan:
    Re-ACK 52f4d567d6
  hebasto:
    re-ACK 52f4d567d6

Tree-SHA512: 0cffd99b4dd4864bf618aa45aeaabbef2b6441d27b6dbb03489c4e013330877682ff17b418d07aa25fbe1040bdf2c67d7559bdeb84128c5437bf0e6247719016

src/qt/sendcoinsdialog.cpp

@@ -203,7 +203,7 @@ void SendCoinsDialog::setModel(WalletModel *_model)
         if (model->wallet().hasExternalSigner()) {
             //: "device" usually means a hardware wallet.
             ui->sendButton->setText(tr("Sign on device"));
-            if (gArgs.GetArg("-signer", "") != "") {
+            if (model->getOptionsModel()->hasSigner()) {
                 ui->sendButton->setEnabled(true);
                 ui->sendButton->setToolTip(tr("Connect your hardware wallet first."));
             } else {