multiprocess: add interfaces::ExternalSigner class

Add interfaces::ExternalSigner to let signer objects be passed between
processes and signer code to run in the original process, without
multiple processes linking and running signer code.

src/qt/createwalletdialog.cpp

@@ -6,7 +6,7 @@
 #include <config/bitcoin-config.h>
 #endif
 
-#include <external_signer.h>
+#include <interfaces/node.h>
 #include <qt/createwalletdialog.h>
 #include <qt/forms/ui_createwalletdialog.h>
 
@@ -113,7 +113,7 @@ CreateWalletDialog::~CreateWalletDialog()
     delete ui;
 }
 
-void CreateWalletDialog::setSigners(const std::vector<ExternalSigner>& signers)
+void CreateWalletDialog::setSigners(const std::vector<std::unique_ptr<interfaces::ExternalSigner>>& signers)
 {
     m_has_signers = !signers.empty();
     if (m_has_signers) {
@@ -126,7 +126,7 @@ void CreateWalletDialog::setSigners(const std::vector<ExternalSigner>& signers)
         ui->blank_wallet_checkbox->setChecked(false);
         ui->disable_privkeys_checkbox->setEnabled(false);
         ui->disable_privkeys_checkbox->setChecked(true);
-        const std::string label = signers[0].m_name;
+        const std::string label = signers[0]->getName();
         ui->wallet_name_line_edit->setText(QString::fromStdString(label));
         ui->buttonBox->button(QDialogButtonBox::Ok)->setEnabled(true);
     } else {

src/qt/createwalletdialog.h

@@ -7,7 +7,12 @@
 
 #include <QDialog>
 
+#include <memory>
+
+namespace interfaces {
 class ExternalSigner;
+} // namespace interfaces
+
 class WalletModel;
 
 namespace Ui {
@@ -24,7 +29,7 @@ public:
     explicit CreateWalletDialog(QWidget* parent);
     virtual ~CreateWalletDialog();
 
-    void setSigners(const std::vector<ExternalSigner>& signers);
+    void setSigners(const std::vector<std::unique_ptr<interfaces::ExternalSigner>>& signers);
 
     QString walletName() const;
     bool isEncryptWalletChecked() const;

src/qt/walletcontroller.cpp

@@ -274,9 +274,9 @@ void CreateWalletActivity::create()
 {
     m_create_wallet_dialog = new CreateWalletDialog(m_parent_widget);
 
-    std::vector<ExternalSigner> signers;
+    std::vector<std::unique_ptr<interfaces::ExternalSigner>> signers;
     try {
-        signers = node().externalSigners();
+        signers = node().listExternalSigners();
     } catch (const std::runtime_error& e) {
         QMessageBox::critical(nullptr, tr("Can't list signers"), e.what());
     }