Move our_claim_txn_waiting_first_conf to pending_claim_requests

Add claimable_outpoints maps.

Both structures are tied and should ensure their mutual consistency.

Pending_claim_requests is cached by original claim txid. Medatada
and per input material should be constant between bumped transactions,
only change should be partial-claiming of outpoints set and block
reorgs.

Due to RBF rules, if an input has been part of an aggregate tx
at first claim try, if we want the bumped tx to land nicely
in the mempool, inputs should be distributed in multiple
bumped tx but still be aggregate in a new bumped tx.

Author: Antoine Riard