Webform computed element post save alter

Thanks for the patch.

When creating a new hook, it needs to be documented in webform.api.php.

Please use an issue fork and merge request.

I agree the WebformComputedBase:postSave method, makes it very difficult to alter a webform submission computed value.

What is also challenging is entity hooks are triggered before element and handler hooks. Reordering entity, element, and handler hook execution is risky.

We could try moving WebformComputedBase:postSave logic to WebformComputedBase:preSave. This could work for the webform_encrypt.module which is using WebformEncryptSubmissionStorage.::doPostSave to encrypt the submission values

Using WebformComputedBase:preSave won't work because people might be relying on sid and serial values.

The webform_encrypt.module might be only the only usecase for new hook.

Instead, maybe the webform_encrypt.module should override WebformComputed::preSave using hook_webform_element_info_alter() and implement the required logic.