wallet: Add `abortOnClose` parameter to tx sending endpoints

Big wallets, with lots of coins, or big transactions that needs lots of coins can take a some time to craft transactions before broadcasting. We get compounding effect when we use fundLocks where multiple requests are also queued.
So allowing new request parameter abortOnClose can work by making sure that transaction creation is done before request closes. If request closes and transaction already was being sent, it will do nothing.

#845

Start by locating the wallet transaction-sending endpoints and their request-close handling; the issue does not name files or tests. Trace how transaction creation and fundLocks are queued, then verify that abortOnClose completes creation before the request closes and has no effect when sending has already started.

Written by the indexing model from the issue text.