Test register_output is called on dependent txn

Test register_output is called on dependent txn

chain::Filter::register_output may return an in-block dependent
transaction that spends the output. Test the scenario where the txdata
given to ChainMonitor::block_connected includes a commitment transaction
whose HTLC output is spent in the same block but not included in txdata.
Instead, it is returned by chain::Filter::register_output when given the
commitment transaction's HTLC output. This is a common scenario for
Electrum clients, which provided filtered txdata.