Problem/Motivation
We should add a dedicated field storage definition class which allows modules to define field storage definitions in hook_entity_field_storage_info() without having a config-field easily.
Proposed resolution
Add a FieldStorageDefinition class that implements FieldStorageDefinitionInterface.
Remaining tasks
Patch.
User interface changes
None.
API changes
Additional builder class for storage definitions.
Data model changes
None.
Out of scope
Any changes to BaseFieldDefinition, @see #3014760: [PP-1] Create an abstract composite field definition/storage definition and update BaseFieldDefinition to use it.