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/init.h

@@ -14,7 +14,7 @@ class Chain;
 class Echo;
 class Ipc;
 class Node;
-class WalletClient;
+class WalletLoader;
 
 //! Initial interface created when a process is first started, and used to give
 //! and get access to other interfaces (Node, Chain, Wallet, etc).
@@ -29,7 +29,7 @@ public:
     virtual ~Init() = default;
     virtual std::unique_ptr<Node> makeNode();
     virtual std::unique_ptr<Chain> makeChain();
-    virtual std::unique_ptr<WalletClient> makeWalletClient(Chain& chain);
+    virtual std::unique_ptr<WalletLoader> makeWalletLoader(Chain& chain);
     virtual std::unique_ptr<Echo> makeEcho();
     virtual Ipc* ipc();
 };