Mark two more core field type's computed properties as internal

Working on it.

Marked 'date' (DateTimeItem) and 'url' (FileUriItem) properties as internal
Created DateTimeItemOverride.php to override DateTimeItem and marked the date property as internal.
Updated FileUriItemOverride.php (already present) to mark the url property as internal.
Please review

This is already implemented in the file. The datetime field’s date and the file_uri field’s url are handled the same way as daterange in tests/src/Kernel/EcosystemSupport/FieldTypeSupportTest.php.

'datetime' => [  
  // 🐛 Core bug: this is the computed equivalent of `value`, should be marked internal.  
  // @todo Give this similar treatment as `daterange` in https://www.drupal.org/project/experience_builder/issues/3512853  
  'date' => FALSE,  
],  
'file_uri' => [  
  // 🐛 Core bug: this is the computed equivalent of `value`, should be marked internal.  
  // @todo Give this similar treatment as `daterange` in https://www.drupal.org/project/experience_builder/issues/3512853  
  'url' => FALSE,  
],  

Let me know if anything else is needed. Thanks!