[5.x] Allow passing computed fields via an associative array

[godismyjudge95]

We have a number of computed properties for a specific collection and our AppServiceProvider is getting rather long with all the computed properties.

This PR helps solve this by allowing for an associative array to be passed as the 2nd parameter:

Collection::computed('properties', [
  'pdf_url' => fn ($entry, $value) => route('properties.pdf', $entry->id()),
  'deletion_date' => fn ($entry, $value) => $this->generateDeletionDate($entry),
]);

Let me know if you'd like me to add tests

[duncanmcclean]

Let me know if you'd like me to add tests

If you can, that would be great!

We have existing tests for computed values in UserContractTests and EntryTest.