To make use of the new mechanism implemented in the patch from the Product Platform team, we need to make some changes on the EntitySchema side.
When parsing statement/qualifier/reference values, Wikibase will take into account the corresponding Property's data type and not only the value type. A data type specific value parser can be registered with the data type definition (here: `EntitySchema`). This will allow serialized `EntitySchema` values to contain `type`: `wikibase-entityid` without being parsed as an `EntityIdValue`.
The changes that are required are:
* New value type
* New parser/deserializer
* Adjust validators
**Acceptance criteria**
[] Users are able to create an EntitySchema data value type statement
[] Users are able to load an EntitySchema data value type statement and it is linked to the EntitySchema
To create a statement using the API sandbox, use the `wbsetclaim` action, let the API sandbox fill in the `token` parameter, and set the `claim` to JSON similar to this:
```lang=json
{"type":"statement","mainsnak":{"snaktype":"value","property":"P592","datavalue":{"type":"wikibase-entityid","value":{"id":"E1"}}},"id":"P592$6dcf36c9-238a-435b-8ead-6fd1915b8548","rank":"normal"}
```
Where `P592` is a property with data type EntitySchema, `6dcf36c9-238a-435b-8ead-6fd1915b8548` is a random UUID (you can get a fresh one from `cat /proc/sys/kernel/random/uuid`), and `E1` is the ID of an existing EntitySchema.