Kill TransactionDetails

[notmandatory]

Kill TransactionDetails, get details of txs via methods from Wallet instead. Ensure rich data we have from bdk_chain can be observed from Wallet.

[evanlinjin]

This will most likely conflict with the work done for #895, please only start after PR #926 is complete!

[LLFourn]

Two places left where TransactionDetails is being used:

1. get_tx should just return a Option<&Transaction> or potentially a TxNode from TxGraph.
2. as a return value from creating a transaction.

removing (1) is higher priority. You could even keep something like it for (2) so you can return the fee/feerate etc. Changing what gets returned here depends on what happens with transaction building.