Create a value object for the return of ComponentTreeHydrated::getValue

@larowlan previously opened an issue for this: 🐛 \Drupal\experience_builder\Plugin\DataType\ComponentTreeHydrated::getValue should not return a response object Active — this was effectively a newer duplicate 😊

Automatically closed - issue fixed for 2 weeks with no activity.

FYI: The DX niceties this brought were slightly reduced in 🐛 ComponentTreeHydrated prevents serialization Active out of necessity.

Related: #3521137-18: Stop storing JSON blobs in XB config entities: improve DX → , which is an outline of how to do something similar for the other field props on the XB field type.