For every peer expose through `getpeerinfo` RPC whether or not we selected them as HB peers, and whether or not they selected us as HB peers.

Suggestion by @gmaxwell.
CNodeState *state = State(nodeid);
    assert(state != nullptr);
    if (!state->hashLastUnknownBlock.IsNull()) {
        const CBlockIndex* pindex = LookupBlockIndex(state->hashLastUnknownBlock);
        if (pindex && pindex->nChainWork > 0) {
            if (state->pindexBestKnownBlock == nullptr || pindex->nChainWork >= state->pindexBestKnownBlock->nChainWork) {
                state->pindexBestKnownBlock = pindex;
            }
            state->hashLastUnknownBlock.SetNull();
        }
    }
}
static void UpdateBlockAvailability(NodeId nodeid, const uint256 &hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {