[wallet] ListCoins: include watch-only for wallets without private keys

This makes them available in GUI coin selection.

Github-Pull: bitcoin#16944
Rebased-From: 40537f0

src/wallet/wallet.cpp

@@ -2631,9 +2631,13 @@ std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins(interfaces::Ch
 
     AvailableCoins(locked_chain, availableCoins);
 
+    // Include watch-only for wallets without private keys
+    const bool include_watch_only = IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
+    const isminetype is_mine_filter = include_watch_only ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
+
     for (const COutput& coin : availableCoins) {
         CTxDestination address;
-        if (coin.fSpendable &&
+        if ((coin.fSpendable || (include_watch_only && coin.fSolvable)) &&
             ExtractDestination(FindNonChangeParentOutput(*coin.tx->tx, coin.i).scriptPubKey, address)) {
             result[address].emplace_back(std::move(coin));
         }
@@ -2646,7 +2650,7 @@ std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins(interfaces::Ch
         if (it != mapWallet.end()) {
             int depth = it->second.GetDepthInMainChain(locked_chain);
             if (depth >= 0 && output.n < it->second.tx->vout.size() &&
-                IsMine(it->second.tx->vout[output.n]) == ISMINE_SPENDABLE) {
+                IsMine(it->second.tx->vout[output.n]) == is_mine_filter) {
                 CTxDestination address;
                 if (ExtractDestination(FindNonChangeParentOutput(*it->second.tx, output.n).scriptPubKey, address)) {
                     result[address].emplace_back(