Keep generated file comments on the first line

[natebosch]

Let linquist continue to find the generated file marker on the first line, the dart format width comment is allowed to be on any line.

Look for the generated file line exactly and when it starts the file insert the dart format comment following it.

[github-actions[bot]]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:source_gen	2.0.1-WIP	ready to publish	source_gen-v2.0.1-WIP

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[marvin-kolja]

This could generally work, but I've seen many users who do not put the generated content line as the first line in their custom header :D

[kevmoo]

We're now in merge conflict land 😕