Would be nice to have more graceful failure of blinding on very big number of outputs (+ other cases, error descriptions)

Right now if transaction with more than 10k outputs is supplied to blindtransaction, the node would crash on assert.

https://github.com/ElementsProject/elements/blob/dd1623af0a4b028175e1078f7ec7a88d78cee8c0/src/blind.cpp#L404

While 10k outputs seem to be non-realistic for blinded transaction, it can happen with software doing payment batching (that was created and tested on non-blinded txs). The developer might be confused why the node crashes. Graceful failure with indication of what is wrong would be nice.

It would also be nice to have more descriptive messages for other failures of blinding, that would greatly improve the debugging experience when working with confidential transactions.