PHP 8.5: Avoid null array keys in PhabricatorEditEngineConfigurationQuery::loadPage()
Summary:
Setting null as an array key is deprecated since PHP 8.5 per https://www.php.net/releases/8.5/en.php: "Using null as an array offset or when calling array_key_exists() is now deprecated. Use an empty string instead."
`PhabricatorEditEngineConfiguration::getID()` can return null when it is a builtin configuration, see e.g. existing null handling in `PhabricatorEditEngineConfiguration::getIdentifier()`.
I didn't investigate the `getPHID()` spiel though.
```
ERROR 8192: Using null as an array offset is deprecated, use an empty string instead at [/var/www/html/phorge/phorge/src/applications/transactions/query/PhabricatorEditEngineConfigurationQuery.php:134]
ERROR 8192: Using null as an array offset is deprecated, use an empty string instead at [/var/www/html/phorge/phorge/src/applications/transactions/query/PhabricatorEditEngineConfigurationQuery.php:143]
```
Closes T16438
Test Plan:
* On PHP 8.5, go to http://phorge.localhost/transactions/editengine/maniphest.task/view/1/ and select "Edit Form Configuration"
* On PHP 8.5, go to http://phorge.localhost/transactions/editengine/transactions.editengine.config/view/2/ and do something to reload that page (for example: select "Change Field Order", then reorder some fields, and click "Save Changes")
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: mainframe98, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T16438
Differential Revision: https://we.phorge.it/D26657