Clean up the rpc method testmempoolaccept #14016

Sorry I didn't see or comment in the initial PR for the RPC method testmempoolaccept, but I think the method could do with some finesse.

1. Don't take an array of transactions

2. Remove allowhighfees

This really shouldn't be a parameter going in, it should be part of the output. e.g. highFeeAlert: true.

3. Additional information like fees/sizes of the transaction (and ideally its entire ancestor cluster) should be returned, similar to what ever the mempool entry stuff has.

IIRC the idea in supporting an array is to test transaction chaining, where transaction B spends an output of transaction A.

Ah, that makes perfect sense. I'll cross if off the list

Another response field that would be very useful is if it could return information about the transactions that would need to be evicted for this transaction to be accepted in the mempool (i.e. rbf'd out transactions).

Also I'm still not a huge fan of the array-of-transaction's going in. It really feels over-engineered especially as it's likely it'll never even get implemented. At the least I think it should be overloaded with a simplified style:

testmempoolaccept $hex

instead of needing to wrap it with a json array (And then unwrap the response)

Related: #13541

Looks like this has been resolved.

~1. Don't take an array of transactions~ I'm still not a huge fan of the array-of-transaction's going in. It really feels over-engineered especially as it's likely it'll never even get implemented.

Has been implemented in #20833.

2. Remove allowhighfees

Removed in #15620.

3. Additional information like fees/sizes of the transaction

Added in #19940.

Closing for now. Please open a new issue for anything new or forgotten.