Payment failures are no longer populated as structured errors, payment failure details not returned

[alexbosworth]

Background

When making a payment using a send to a route directly, a payment failure normally would return a structured failure message with the failure code

This return value has changed to no longer return a structured failure, it now populates an unstructured error that is missing failure details.

Ideally the behavior for payment failures such as paying to an unknown payment hash remains consistent, and the full set of failure data is returned to the sender

The removal of structured failure data seems to have happened in #5332 with commit cf2b5744a155c02b34ccb0e1d062f5e70e6fa7b4

Your environment

• lnd 0.13.1-beta rc1

Steps to reproduce

• send from node a to node b, using a random payment hash

Expected behavior

• a detailed failure response should be returned, and no error

Actual behavior

• a terse error is returned with a string and no structured failure data