Merge bitcoin/bitcoin#23006: multiprocess: Add new bitcoin-gui, bitcoin-qt, bitcoin-wallet init implementations

d5f985e51f multiprocess: Add new bitcoin-gui, bitcoin-qt, bitcoin-wallet init implementations (Russell Yanofsky)

Pull request description:

  Add separate `interfaces::Init` subclasses for `bitcoin-wallet`,  `bitcoin-gui`, and `bitcoin-qt` binaries instead of sharing `bitcoind` and `bitcoin-node` init subclasses in different binaries. After this, the new init subclasses can be customized in #10102, so node and wallet code is dropped from the `bitcoin-gui` binary and wallet code is dropped from into the `bitcoin-node` binary.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

ACKs for top commit:
  lsilva01:
    reACK d5f985e
  hebasto:
    re-ACK d5f985e51f, only suggested changes since my [previous](https://github.com/bitcoin/bitcoin/pull/23006#pullrequestreview-787537444) review.

Tree-SHA512: 6784210bd9ce3a6fbc66852680d0e9bc513c072dc538aeb7f48cb6a41580d3f567ccef04f975ee767a714a4b05d4d87273e94a79abda1b9c25d5ac4bbe752006

src/bitcoin-wallet.cpp

@@ -8,6 +8,7 @@
 
 #include <chainparams.h>
 #include <chainparamsbase.h>
+#include <interfaces/init.h>
 #include <logging.h>
 #include <util/system.h>
 #include <util/translation.h>
@@ -84,6 +85,13 @@ int main(int argc, char* argv[])
     util::WinCmdLineArgs winArgs;
     std::tie(argc, argv) = winArgs.get();
 #endif
+
+    int exit_status;
+    std::unique_ptr<interfaces::Init> init = interfaces::MakeWalletInit(argc, argv, exit_status);
+    if (!init) {
+        return exit_status;
+    }
+
     SetupEnvironment();
     RandomInit();
     try {