Plugins now use the 'context_definitions' key to define their contexts

Many plugin types require context information to operate correctly. Individual plugins can define their required context definitions in their annotation using the 'context' key, like so:

<?php

/**
 * Provides a 'User Role' condition.
 *
 * @Condition(
 *   id = "user_role",
 *   label = @Translation("User Role"),
 *   context = {
 *     "user" = @ContextDefinition("entity:user", label = @Translation("User"))
 *   }
 * )
 */
class UserRole extends ConditionPluginBase {}

As of #3014949: Deprecate 'context' on Block and Condition plugin annotations in favor of 'context_definitions', the 'context' key is deprecated and replaced by 'context_definitions', which more accurately describes the contents of the array. The correct way for plugins to define context definitions is like so:

<?php

/**
 * Provides a 'User Role' condition.
 *
 * @Condition(
 *   id = "user_role",
 *   label = @Translation("User Role"),
 *   context_definitions = {
 *     "user" = @ContextDefinition("entity:user", label = @Translation("User"))
 *   }
 * )
 */
class UserRole extends ConditionPluginBase {}