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/interfaces/node.h

@@ -37,7 +37,7 @@ struct bilingual_str;
 
 namespace interfaces {
 class Handler;
-class WalletClient;
+class WalletLoader;
 struct BlockTip;
 
 //! Block and header tip information
@@ -187,8 +187,8 @@ public:
     //! Broadcast transaction.
     virtual TransactionError broadcastTransaction(CTransactionRef tx, CAmount max_tx_fee, std::string& err_string) = 0;
 
-    //! Get wallet client.
-    virtual WalletClient& walletClient() = 0;
+    //! Get wallet loader.
+    virtual WalletLoader& walletLoader() = 0;
 
     //! Register handler for init messages.
     using InitMessageFn = std::function<void(const std::string& message)>;
@@ -210,7 +210,7 @@ public:
     using ShowProgressFn = std::function<void(const std::string& title, int progress, bool resume_possible)>;
     virtual std::unique_ptr<Handler> handleShowProgress(ShowProgressFn fn) = 0;
 
-    //! Register handler for wallet client constructed messages.
+    //! Register handler for wallet loader constructed messages.
     using InitWalletFn = std::function<void()>;
     virtual std::unique_ptr<Handler> handleInitWallet(InitWalletFn fn) = 0;