defaultStorageSettings() and defaultFieldSettings() should document that they must not have setting names in common

Explanation:

In Drupal 11, the FieldItemInterface includes two methods: defaultFieldSettings() and defaultStorageSettings(). These methods define default settings for field items at different levels:

- defaultFieldSettings(): Specifies default settings at the field level.
- defaultStorageSettings(): Specifies default settings at the storage level.

Issue:

The methods are expected to return settings with unique names. This is crucial because other parts of the core, like BaseFieldDefinition, merge these arrays. Overlapping names can lead to conflicts or unexpected behavior.

Solution:

Document in both methods that setting names must be distinct to avoid such issues.

We are going to take this issue as part of the Symetris → contribution workshop.