Fix DataType::$constraint docs that reference method that does not exist

Problem/Motivation

The DataType annotation documents $constraints and points people to the getConstraints() method that no longer exists on TypedDataManager. In fact the $constraints property on data types does not seem to be used in core as data definitions are used to add and enforce constraints. TypedData::getConstraints uses its definition's constraints rather than any provided on the annotation.

TypedDataInterface::getConstraints only explains that it should get constraints, and how it is done is left to the implementation so it is possible that a data type could implement constraint getting from the annotation.

Current documentation:

  /**
   * An array of validation constraints for this type.
   *
   * @var array
   *
   * @see \Drupal\Core\TypedData\TypedDataManager::getConstraints().
   */
  public $constraints;

This could be rolled into #2047119: Remove deprecated documentation in DataType annotation → , but unsure of the scope of that issue as it is a follow-up to #2002102: Move TypedData primitive types to interfaces → .

Proposed resolution

• Clarify that $constraints is not used normally and remove the @see TypedDataManager::getConstraints(), and clarify that a data type uses constraints from its data definition by default.
  • Any additional explanation about implementing constraints or using $constraints property (if it isn't deprecated) should go on the Data Type Plugin docs page → .
• Decide whether or not to deprecate $constraints property on DataType annotation.

Remaining tasks

Need to decide approach to take.

User interface changes

N/A

API changes

Yes, If we deprecate $constraints property in the annotation, then it will be removed in a later version.

Data model changes

N/A