[dartdev] Don't fix Pubspec issues unless no codes are given, or a pubspec-related code is given

Previously, the pubspec fixes would always run, even if you had asked only for a specific code to be fixed. This change has Pubspec fixes only run if there are no explicit codes, or the codes include the Pubspec diagnostic being fixed (`missing_dependency`, 'depend_on_referenced_package', 'migrate_design_widgets').

Additionally, relax the requirement for there to have been Dart fixes in order to apply Pubspec fixes.

Fixes https://github.com/dart-lang/sdk/issues/60871
Fixes https://github.com/dart-lang/sdk/issues/64156

Change-Id: Ic81497c13cd8b4d156fbfb0ae6d09628d039edd9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/544161
Reviewed-by: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>