RPC: listunspent, add "include immature coinbase" flag

so we can return the immature coinbase UTXOs as well.

test/functional/wallet_balance.py

@@ -77,8 +77,18 @@ class WalletTest(BitcoinTestFramework):
         self.log.info("Mining blocks ...")
         self.generate(self.nodes[0], 1)
         self.generate(self.nodes[1], 1)
+
+        # Verify listunspent returns immature coinbase if 'include_immature_coinbase' is set
+        assert_equal(len(self.nodes[0].listunspent(query_options={'include_immature_coinbase': True})), 1)
+        assert_equal(len(self.nodes[0].listunspent(query_options={'include_immature_coinbase': False})), 0)
+
         self.generatetoaddress(self.nodes[1], COINBASE_MATURITY + 1, ADDRESS_WATCHONLY)
 
+        # Verify listunspent returns all immature coinbases if 'include_immature_coinbase' is set
+        # For now, only the legacy wallet will see the coinbases going to the imported 'ADDRESS_WATCHONLY'
+        assert_equal(len(self.nodes[0].listunspent(query_options={'include_immature_coinbase': False})), 1 if self.options.descriptors else 2)
+        assert_equal(len(self.nodes[0].listunspent(query_options={'include_immature_coinbase': True})), 1 if self.options.descriptors else COINBASE_MATURITY + 2)
+
         if not self.options.descriptors:
             # Tests legacy watchonly behavior which is not present (and does not need to be tested) in descriptor wallets
             assert_equal(self.nodes[0].getbalances()['mine']['trusted'], 50)