multiprocess: Delay wallet client construction

Delay wallet client construction until after logging, thread and other
init for two reasons:

- More responsive multiprocess GUI startup. When bitcoin-gui is started
  this moves the call from bitcoin-gui to bitcoin-node that spawns
  bitcoin-wallet off of the GUI event thread and onto the background GUI
  init executor thread.

- Avoids feature_logging.py test failures with bitcoin-node by making
  bitcoin-wallet logging start after bitcoin-node logging starts,
  because the tests are not written to handle the bitcoin-wallet logging
  init code running first.

This partially reverts commit b266b3e0bf,
moving wallet client creation back to the place it was located before.

src/qt/bitcoin.cpp

@@ -271,7 +271,6 @@ void BitcoinApplication::createSplashScreen(const NetworkStyle *networkStyle)
     // We don't hold a direct pointer to the splash screen after creation, but the splash
     // screen will take care of deleting itself when finish() happens.
     m_splash->show();
-    connect(this, &BitcoinApplication::requestedInitialize, m_splash, &SplashScreen::handleLoadWallet);
     connect(this, &BitcoinApplication::splashFinished, m_splash, &SplashScreen::finish);
     connect(this, &BitcoinApplication::requestedShutdown, m_splash, &QWidget::close);
 }

src/qt/splashscreen.cpp

@@ -194,6 +194,7 @@ void SplashScreen::subscribeToCoreSignals()
     // Connect signals to client
     m_handler_init_message = m_node->handleInitMessage(std::bind(InitMessage, this, std::placeholders::_1));
     m_handler_show_progress = m_node->handleShowProgress(std::bind(ShowProgress, this, std::placeholders::_1, std::placeholders::_2, std::placeholders::_3));
+    m_handler_init_wallet = m_node->handleInitWallet([this]() { handleLoadWallet(); });
 }
 
 void SplashScreen::handleLoadWallet()

src/qt/splashscreen.h

@@ -66,6 +66,7 @@ private:
     bool m_shutdown = false;
     std::unique_ptr<interfaces::Handler> m_handler_init_message;
     std::unique_ptr<interfaces::Handler> m_handler_show_progress;
+    std::unique_ptr<interfaces::Handler> m_handler_init_wallet;
     std::unique_ptr<interfaces::Handler> m_handler_load_wallet;
     std::list<std::unique_ptr<interfaces::Wallet>> m_connected_wallets;
     std::list<std::unique_ptr<interfaces::Handler>> m_connected_wallet_handlers;