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.cpp

@@ -11,7 +11,7 @@
 namespace interfaces {
 std::unique_ptr<Node> Init::makeNode() { return {}; }
 std::unique_ptr<Chain> Init::makeChain() { return {}; }
-std::unique_ptr<WalletClient> Init::makeWalletClient(Chain& chain) { return {}; }
+std::unique_ptr<WalletLoader> Init::makeWalletLoader(Chain& chain) { return {}; }
 std::unique_ptr<Echo> Init::makeEcho() { return {}; }
 Ipc* Init::ipc() { return nullptr; }
 } // namespace interfaces