[8.x] Add commonmark as recommended package for Illuminate\Support

[timacdonald]

league/commonmark is a required package when using the Str::markdown() and $stringable->markdown() methods.

illuminate/support when used outside of laravel/framework does not require league/commonmark in it's composer.json.

Added as a suggested package, which seems to be the home for others like this, such as ramsey/uuid.

PR that introduced of these methods: #36071

[GrahamCampbell]

Is this missing on 6.x?

[timacdonald]

Is this missing on 6.x?

I've just checked 6.x and 7.x and neither of them have this in their composer.json, however these markdown method were only added to 8.x, so unless there was another reason for it to exist in the previous versions, I think that makes sense...unless I'm misunderstanding the question.

Let me know. Happy to make any required tweaks.

[driesvints]

It's only needed for 8.x