Figure out how to encapsulate writable settings supplied by DataDefinitionInterface

Assigning this to the field system component because that's where I came at it from. Please update as needed.

Problem/Motivation

I want to encapsulate the public properties of FieldConfigBase, as per #2030637: Expand FieldConfig/BaseFieldOverride/FieldConfigBase with methods → . FieldConfigBase implements DataDefinitionInterface.

This is difficult because DataDefinitionInterface doesn't allow for $settings to be protected or private, since it only supports a getter and not a setter.

Proposed resolution

Add setSettings() and setSetting() to DataDefinitionInterface, or perhaps create another interface with a name less cumbersome than DataDefinitionWithWritableSettingsInterface.

Remaining tasks

Waiting for a namespace, see #17 🐛 Figure out how to encapsulate writable settings supplied by DataDefinitionInterface Closed: outdated so that patch can be updated.

User interface changes

API changes