- 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
This is a backport of Core PR18895 [2/4]
https://github.com/bitcoin/bitcoin/pull/18895/commits/a7ebe48b94c5a9195c8eabd193204c499cb4bfdb
Depends on D9023