Fix EZP-19650: move to trash and trashpurge.php can hit the memory limit

Bug: https://jira.ez.no/browse/EZP-19650
*DO NOT MERGE YET, WAITING FOR FEEDBACK FROM THE CUSTOMER*

Description
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While purging the trash (or putting a content object in the trash), `eZContentObject::allContentObjectAttributes` is used to load all content object attributes from all versions of the content object that is being removed. If this content object has a lots of attributes and/or attributes with a lots of data (big eztext, ezxmltext, ...) and/or versions, this might required too much memory.

This patch changes the way the content attributes are loaded to not load all of them in one go.


Test
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Manual tests