Publish warning for `analysis_server_plugin` plugins

[FMorschel]

I wasn't sure if this validation was local or remote (pub.dev), but I'm guessing local.

Problem

When publishing analysis_server_plugin plugins, we get this warning:

Package validation found the following potential issue:

• The name of "lib\main.dart", "main", should match the name of the package, "<package>".
  This helps users know what library to import.

Publishing is forever; packages cannot be unpublished.
Policy details are available at https://pub.dev/policy

Expected behavior

I was expecting this warning to be flipped for analysis_server_plugin plugins, so we warn when there is no main.dart file. Since that is what the server will be looking for.

At the very least, I think this current warning could be suppressed.

CC @srawlins

[srawlins]

+1; it'd be nice to have an exception for packages that depend on analysis_server_plugin.

[sigurdm]

This sounds like something we should fix. How do we know if a package is a plugin?

[FMorschel]

At the very least they should depend on analysis_server_plugin and preferably they already have a main.dart file with a plugin top level getter. Because that's where the server will start it from.