Magic getters/setters support for fieldable Apigee entities

[mxr576]

Is your feature request related to a problem? Please describe.

$entity->field_foo->getValue() is a commonly used Drupal trick for accessing field data on an entity instead of using (just a bit longer) $entity->get('field_foo')->getValue() . Not supporting these magic methods only becomes a problem on fieldable Apigee entities when Drupal core/contrib codes are called on them. like when an entity reference field on an Apigee entity gets validated by ValidReferenceConstraintValidator.

Steps to reproduce

• Add an API Product reference field to a Team entity
• Create a team and reference an API product in the field
• Edit the team and reference a new API product in the field --> WSOD

Describe the solution you would like

Add support for magic __get()/__set() methods to fieldable Apigee entities.

Describe alternatives you have considered

Additional context

• They are planned to be deprecated/removed from Drupal core \o/ but until that time comes...