Add support for serialization of snak hashes

[lucaswerkmeister]

SnakSerializer and SnakDeserializer gain support for serializing / deserializing the hash of a snak. (Serializing hashes is not required when sending serializations to the API, but the Wikibase view code assumes that serialization+deserialization is a lossless roundtrip, so if we don’t serialize it, the hash is lost when setting a new snak on a snakview.)

[manicki]

Seems reasonable!

[thiemowmde]

The changes made in this patch are perfectly fine. But since the JavaScript DataModel classes don't support the additional hash parameter yet, this should fail. There should be at least a single, trivial test that fails right now, and succeeds the moment wmde/WikibaseDataModelJavaScript#77 is merged, released, and required via composer.json in this patch here.

I'm willing to continue working on this series of patches the next days if you don't have the time.

[lucaswerkmeister]

Uhm… I’m pretty sure that any test that uses SnakSerializer should fail because it calls the nonexistent method snak.getHash()… but apparently there’s no easy way to run the tests and they’re not part of CI?

[thiemowmde]

You are right, the tests already fail because of the getHash call. But CI does not run the tests.

However, this patch should not be merged before the relevant change to the DataModel component is made, released, and the requirement in this components composer.json can be updated.