Deprecration messages are logged to the stdout

[theofidry]

Bug Report

Subject	Details
Rector version	2.3.8

I could not find where this is done in the codebase, but it appears the deprecration messages are logged to the stdout. In and of itself, that is fine. However, if one uses --output-format=gitlab for instance, those deprecrations are part of the output that may be piped, breaking the format.

Minimal PHP Code Causing Issue

• register a deprecrated rule as a skipped rule, e.g. withSkip([\Rector\Php81\Rector\Array_\FirstClassCallableRector::class])
• Exectued rector process --dry-run --output-format=gitlab | jq -> jq fails because the piped output is not a JSON

When the output is not piped, we get:

$ rector process --dry-run --output-format=gitlab


 [WARNING] These rules are skipped, but are deprecated. Most likely you do not need to skip them anymore as not part of
           any set and remove them:

           * Rector\Php81\Rector\Array_\FirstClassCallableRector


[]

 [WARNING] Skipped rule "Rector\Php81\Rector\Array_\FirstClassCallableRector" is deprecated



 [WARNING] This skipped rule is never registered. You can remove it from "->withSkip()"


 * Rector\Php81\Rector\Array_\FirstClassCallableRector

You can see all those plain text messages are piped too, breaking the JSON.

Expected Behaviour

I think the simplest way to go about it is to log it to the stderr, and if no stderr is available and a dedicated format output is passed, either it needs to be adjusted to that output format (I do not know if such deprecrations can be passed to the gitlab format for example) or omitted (it is a loss of information, but at least it won't crash).

[TomasVotruba]

Seems like a good approach. Care to send PR?

[theofidry]

@TomasVotruba drafted rectorphp/rector-src#7914 but I stopped as there is a few questions