Customization of collection row form styling

[weaverryan]

See symfony/symfony#4909 - I don't think this is a detail we have in the docs currently.
#1998 is related, but I don't believe the approach is the "correct" one (but it's been some time since I reviewed it). We should look at symfony/symfony#4909 and include an entry in the form_collections doc about how to correctly customize the styling of a collection row.

[wouterj]

#1998 has been replaced by #4629 The suggestion of stof mentioned in the PR seems to be the correct way.

[wouterj]

Eventually, this is now fixed by #4629