Incorrect typehint documentation for FieldItemInterface::view() and FieldItemListInterface::view(): $display_options could also be a string

Problem/Motivation

Using phpstan on a project revealed that the signature of \Drupal\Core\Field\FieldItemInterface::view() and \Drupal\Core\Field\FieldItemListInterface::view() are incorrect.

They both have the following phpdoc for the $display_options argument:

   * @param array $display_options
   *   Can be either the name of a view mode, or an array of display settings.
   *   See EntityViewBuilderInterface::viewField() for more information.

The type should be string|array instead of just array to be consistent with the description and with EntityViewBuilderInterface::viewField().

Proposed resolution

Fix the type hint.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

Not needed?