fix: include error message in --json output

[spokodev]

Closes #1608.

When a command with enableJsonFlag errors, --json mode serializes the error via toErrorJson(), which returned {error: err}. JSON.stringify (in logJson) then drops Error.prototype.message/.name/.stack because they are non-enumerable own properties, so the user-facing message is lost:

$ mycmd --json          # throw new Error('...')
{ "error": {} }
$ mycmd --json          # throw new Errors.CLIError('...')
{ "error": { "oclif": { "exit": 2 } } }

This affects all three idiomatic patterns: throw new Error(...), throw new Errors.CLIError(...), and this.error(...).

Fix

In toErrorJson, when the error is an Error, serialize message/name explicitly while spreading enumerable own properties, so existing structural fields (e.g. a CLIError's oclif metadata) are preserved and the message is surfaced. Non-Error values are passed through unchanged.

Tests

Two --json error rendering tests, red before the change and green after — a plain Error and a CLIError (asserting the message is present and oclif.exit is still emitted). Full test/command + test/errors suites pass.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @spokodev to sign the Salesforce Inc. Contributor License Agreement.

[jfeingold35]

@spokodev , thank you for submitting this. I'll get it reviewed and QA'd, and then assuming nothing needs to change, we can merge it and close the associated Issue.

[jfeingold35]

@spokodev , the PR looks good. Assuming the tests all pass, we'll be good to merge it.