Determine how to test for data integrity proofs when VC might contain multiple proofs conforming to another spec

[aljones15]

Verifiable Credentials can contain multiple proofs signed by different issuers and signature suites.

In the case of this library I think we should focus on this:

• Pass in a type that we testing for such as Ed25519Signature2020.
• Filter the VC's proofs so that we are only testing on proofs with the expected type
• If the filtered proofs array has a length 0 or less then fail all assertions
• Otherwise we test every proof in the filtered Array for data integrity

[aljones15]

solution to this is assert on any proof with type DataIntegrityProof