feat: #3620922 Allow data definitions to declare example values

Closes #3620922

Add getExamples() to DataDefinitionInterface and setExamples() to DataDefinition. Examples are stored under the 'examples' definition key. getExamples() returns an empty array when no examples are declared.

Examples are metadata only. TypedDataManager::create(), applyDefaultValue() and validation do not use them.

FieldConfigBase implements the interface without extending DataDefinition and returns no examples. BaseFieldOverride forwards to its base field definition.

Generated with the help of an LLM.