Feature request: dry-run (or export txhex?) for sendcoins

[Overtorment]

dry-run (or export txhex?) for sendcoins would allow outer code to validate & decide if its feasible to broadcast resulting transaction.
that could prevent issues like #6556 for people that know what they are doing

[Roasbeef]

The main routine we use for sending coins on chain has a dryRun field which was made in part of this purpose. So adding this feature would entail threading that new arg from the CLI/RPC to the main call site.

[alexbosworth]

potentially related to a potential call to test policy limits against the backing chain daemon: #6309