scripted-diff: Rename interfaces::WalletClient to interfaces::WalletLoader

Name has been confusing since it was introduced, and it was pointed in
recent review club as https://bitcoincore.reviews/10102 that it was
particularly unclear how interfaces::WalletClient was different from
interfaces::Wallet.

-BEGIN VERIFY SCRIPT-
ren() { git grep -l "$1" src | xargs sed -i "s/$1/$2/g"; }
ren WalletClient WalletLoader
ren walletClient walletLoader
ren wallet_client wallet_loader
ren "wallet clients release the wallet" "wallet pointer owners release the wallet"
ren "wallet client" "wallet loader"
ren "Wallet client" "Wallet loader"
-END VERIFY SCRIPT-

src/node/interfaces.cpp

@@ -63,7 +63,7 @@ using interfaces::FoundBlock;
 using interfaces::Handler;
 using interfaces::MakeHandler;
 using interfaces::Node;
-using interfaces::WalletClient;
+using interfaces::WalletLoader;
 
 namespace node {
 namespace {
@@ -280,9 +280,9 @@ public:
     {
         return BroadcastTransaction(*m_context, std::move(tx), err_string, max_tx_fee, /*relay=*/ true, /*wait_callback=*/ false);
     }
-    WalletClient& walletClient() override
+    WalletLoader& walletLoader() override
     {
-        return *Assert(m_context->wallet_client);
+        return *Assert(m_context->wallet_loader);
     }
     std::unique_ptr<Handler> handleInitMessage(InitMessageFn fn) override
     {