Fix broken taskprocessing api /tasktypes endpoint

[julien-nc]

Reported by @alperozturk96 💙

The /ocs/v2.php/taskprocessing/tasktypes was broken by #49015 which changed objects into arrays in the inputShape, outputShape, optionalInputShape etc...

• Those changes have been reverted
• Make sure the serialization of the response gives empty objects instead of empty arrays
• Generate OpenAPI specs

@provokateurin Please put at least @marcelklehr or me as reviewers when making such changes.

[provokateurin]

stdClass class missing

[oleksandr-nc]

@provokateurin Please put at least @marcelklehr or me as reviewers when making such changes.

Maybe we need a more precise CODEOWNERS file so that this can be done automatically? (it's hard to remember who is responsible for which file and everyone needs to remember it, which is almost impossible)