Fix file upload when using 'nuxeo-dropzone' element in edit layout

When using the nuxeo-dropzone element in the edit layout of a document for a Blob property other than file:content or files:files, the file is properly uploaded using the batch uploader but does not get attached to the document, the payload of the PUT request does not mention the blob property supposed to contain the blob:

{"entity-type":"document","uid":"cc86082d-c0fd-4c6c-85ff-950c9496de57","properties":{}}

How to reproduce:

• create a new document type named Doctype1 with a Blob property named doctype1:blobprop
• define the create layout, metadata layout, and the edit layout In Studio Designer
• use the following code in the edit layout for the Blob property:

      <nuxeo-dropzone role="widget" label="XML Script" name="properties" xpath="doctype1:blobprop" document="[[document]]"></nuxeo-dropzone>
  

• deploy to a Nuxeo instance
• log in the Web UI and create a document of type Doctype1 in a Workspace
• edit the created document and drag and drop a file in the drop zone

Expected result: the file gets attached to the document in property doctype1:blobprop.
Actual result: the file does not get attached to the document and property doctype1:blobprop is null.

It seems a first attempt to fix this was done in NXP-25362.