Use migration name or group name as page title

This is failing because of PHP 7.4.
Time to ditch this php version?

My latest PR still has some problems.
The group argument in some cases is just a string, so the title callback expecting an object as parameter won't work.
We should do different title callbacks for different routes.

Also, we get distinct items in the breadcrumb for:
- /admin/structure/migrate/manage/GROUP
- /admin/structure/migrate/manage/GROUP/migrations

We should put a different title into the breadcrumb than the page title.

There should be a distinct route setting for "breadcrumb title callback" or perhaps "navigation title callback".

We can set the title directly in a controller like:

return [
  '#title' => $migration->label(),
  'content' => $build,
];

But this does not work that easily for entity form pages where we don't own the controller.

Needs a rebase

Working on the rebase.

Rebased, and also resolved the pipeline errors,
Please review!!

This looses the edit, overview, etc context. It is nice to add the name, but it is also nice to include that context from what was there before. Can we retain both?

I updated the title callback to retain the page context and include the migration/group label.
Please review!!

Initially from looking at https://www.drupal.org/docs/drupal-apis/routing-system/structure-of-routes → => _title_arguments I thought this could be a more simple solution. But you can't mix title callbacks and arguments together. I did leave one bit of feedback on the MR.

Updated the code according to the comment.
Please review!!