feat: Document the add of IRichTextFormatter to OCP in 31

Signed-off-by: Côme Chilliet <[email protected]>

Author: come-nc

developer_manual/app_publishing_maintenance/app_upgrade_guide/upgrade_to_31.rst

@@ -124,6 +124,7 @@ Added APIs
   be called automatically based on the supported MIME types. An app may register as many of these as needed.
 - New events ``OCP\User\Events\BeforeUserIdUnassignedEvent``, ``OCP\User\Events\UserIdUnassignedEvent``, and ``OCP\User\Events\UserIdAssignedEvent`` have been added to replace the hooks ``\OC\User::preUnassignedUserId``, ``\OC\User::postUnassignedUserId`` and ``\OC\User::assignedUserId``.
 - New interface ``OCP\Files\Storage\IConstructableStorage`` for storages that can be built by passing only an array to the constructor.
+- New service ``OCP\RichObjectStrings\IRichTextFormatter`` to format rich text into parsed plain text using its ``richToParsed`` method.
 
 Changed APIs
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