[rpc] add unbroadcast info to mempool entries and getmempoolinfo

- expose info about number of txns in unbroadcast set and whether a mempool entry's tx has passed initial broadcast
- makes rpcs more informative and allows for more explicit testing, eg tracking if tx is in unbroadcast set
before and after originating node connects to peers (adds this in mempool_unbroadcast.py)
- adds mempool method IsUnbroadcastTx to query for tx inclusion in  mempool's unbroadcast set

test/functional/mempool_packages.py

@@ -212,6 +212,10 @@ class MempoolPackagesTest(BitcoinTestFramework):
         for tx in chain[:MAX_ANCESTORS_CUSTOM]:
             assert tx in mempool1
         # TODO: more detailed check of node1's mempool (fees etc.)
+        # check transaction unbroadcast info (should be false if in both mempools)
+        mempool = self.nodes[0].getrawmempool(True)
+        for tx in mempool:
+            assert_equal(mempool[tx]['unbroadcast'], False)
 
         # TODO: test ancestor size limits