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/node/ui_interface.h

@@ -82,6 +82,9 @@ public:
     /** Progress message during initialization. */
     ADD_SIGNALS_DECL_WRAPPER(InitMessage, void, const std::string& message);
 
+    /** Wallet client created. */
+    ADD_SIGNALS_DECL_WRAPPER(InitWallet, void, );
+
     /** Number of network connections changed. */
     ADD_SIGNALS_DECL_WRAPPER(NotifyNumConnectionsChanged, void, int newNumConnections);