More info about pub publish validations

[MaryaBelanger]

https://dart.dev/tools/pub/cmd/pub-lish

pub publish completes several layers of validation that would be worth describing on it's page (not much other info there currently)

Ideally will redo / undo this change because it doesn't really make sense to only mention that one kind of validation in the publishing step, because:

1. many different kinds of validations happen, not just the clean git state, and
2. validations happen for both test publishing and real publishing, but that PR only adds the validation to the "real" publishing section.

It'd be better to have either a short section about validations before both the test publish and real publish sections, or a section about validation on the command page that those sections can link to, or both.

[MaryaBelanger]

@sigurdm are all the validators here run for pub publish or are some of them related to different pub commands?

[sigurdm]

@sigurdm are all the validators here run for pub publish or are some of them related to different pub commands?

Yes they are, but the source of truth would be this list:
https://github.com/dart-lang/pub/blob/master/lib/src/validator.dart#L143