Implement the new entity field API for the list field type

A first patch. Add the item classes and converted a basic test to it.

This should fix the test failure.

This patch adds a dependency to options.module on number and text. Conceptually, that makes sense to me, because this module basically provides extended versions of the integer/float/text field types.

The other question is here if we need more tests. We're not adding new field item type classes, so IMHO adding more unit tests for those would be pointless. As said above, there are a lot of tests for allowed values, callbacks and similar things that I'm already in the process of converting to NG in #1822000: Remove Drupal\field_test\Plugin\Entity\Type\TestEntity in favor of EntityTest.

This looks pretty good to me, and I know I need the 'field item class' definitions for #1818556: Convert nodes to the new Entity Field API.
So even if I just mainly did a visual review I'm bold enough to set this RTBC.

Raising priority since this is blocking a critical task: #1818556: Convert nodes to the new Entity Field API.

Patch looks good the me as well. I agree that we want this dependencies to be able to re-use the existing fields.

Being forced to introduce a dependency on number module is a little unfortunate, but otherwise this looks good, and allows us to make progress on the node patch.

Committed and pushed to 8.x. Thanks!