This adds 3 new RPC calls (getancestors getmempoolancestors, getdescendants getmempooldescendants, getmempoolentry) to expose more mempool information over RPC.
Now that we have policy rules that are tied to transaction chains (including limits on the number of in-mempool ancestors and in-mempool descendants, and mempool eviction and RBF policies that depend on fees of descendants), it seems helpful to be able to expose more information about the chains a given tx is part of over RPC.
This is motivated by the discussion in #7222. @petertodd You mentioned wanting to see specific use-cases for this information; I think there are clear improvements to the fee-bumping tools in your replace-by-fee repo that could be made if we had these functions (the first two tools I looked at just now don’t seem to consider transaction chains at all in fee calculations?). I’ll try to post a link in this PR to specific proposed improvements when I have something to share that will demonstrate this more clearly.