Add test vectors that use i18n strings

[msporny]

Transferring this issue from w3c/vc-data-integrity#218:

The test vectors use human-readable strings and the i18n group requested that we express them using the appropriate @language/@direction values across vc-data-integrity, vc-di-eddsa, and vc-di-ecdsa. This is a tracking issue to make sure we update the test vectors to conform to i18n guidance.

[aljones15]

@msporny The current spec does not contain any @language or @direction statements or even a mention of those features. The VC Data Model spec does at least mention @language and @direction.

So adding this feature to D.I. is not that hard (existing tests already exist in VC Data Model for this), the question is should the il8n examples be done as a feature that a suite or implementer can turn on to ensure conformance or should il8n be on by default in all suites? I believe the former makes more sense as no normative statement in DI says an implementer MUST support il8n. Additionally, should the il8n properties be on a data integrity proof (the subject of this test suite) or do we need to demonstrate that VCs with il8n properties can be signed with data integrity proofs?

{
  "type": "DataIntegrityProof",
  "id": "urn:uuid:26329423-bec9-4b2e-88cb-a7c7d9dc4544",
  "cryptosuite": "eddsa-rdfc-2022",
  "created": "2023-02-26T22:06:38Z",
  "verificationMethod": "did:key:z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7#z6MktgKTsu1QhX6QPbyqG6geXdw6FQCZBPq7uQpieWbiQiG7",
  "proofPurpose": {
     "@value":" assertionMethod",
     "@language": "en",
     "@direction": "ltr"
  },
  "proofValue": "z5gL4Hy8N4B6zr9mQAGqpsry1iTdxEAp4zjqPNQv7iTvgdkMcHKnMALvPwU3YAKZhYn3k3Jmut2TAMxSaHaggFtf4"
}

only proofPurpose and maybe cryptosuite make sense as il8n values unless we want to express dates in non-arabic numbers.