Bugfix: Wallet: Lock cs_wallet for SignMessage

cs_desc_main is typically locked within scope of a cs_wallet lock, but:

CWallet::IsLocked locks cs_wallet
...called from DescriptorScriptPubKeyMan::GetKeys
...called from DescriptorScriptPubKeyMan::GetSigningProvider which locks cs_desc_main first, but has no access to cs_wallet
...called from DescriptorScriptPubKeyMan::SignMessage
...called from CWallet::SignMessage which can access and lock cs_wallet

Resolve the out of order locks by grabbing cs_wallet in CWallet::SignMessage first

src/wallet/wallet.cpp

@@ -2588,6 +2588,7 @@ SigningResult CWallet::SignMessage(const std::string& message, const PKHash& pkh
     CScript script_pub_key = GetScriptForDestination(pkhash);
     for (const auto& spk_man_pair : m_spk_managers) {
         if (spk_man_pair.second->CanProvide(script_pub_key, sigdata)) {
+            LOCK(cs_wallet);  // DescriptorScriptPubKeyMan calls IsLocked which can lock cs_wallet in a deadlocking order
             return spk_man_pair.second->SignMessage(message, pkhash, str_sig);
         }
     }