refactor(credential-w3c): remove hardcoded proof formats

[nickreynolds]

What issue is this PR fixing

• Currently, it's impossible to add support for new proof formats without forking Veramo because the different logic for each supported proof format is hard-coded into credential-w3c

What is being changed

• A new package (credential-jwt) was created to pull JWT-specific logic out of credential-w3c
• The CredentialIssuer plugins (credential-jwt, credential-ld, credential-eip712) now implement a new shared interface (IProofFormatIssuerVerifier) to allow credential-w3c to call appropriate agent functions without knowing their names
• credential-w3c constructor now accepts an array of IProofFormatIssuerVerifier plugins and iterates over them to perform the correct logic when creating or verifying credentials or presentations

Quality

Check all that apply:

• [ ] I want these changes to be integrated
• [X] I successfully ran pnpm i, pnpm build, pnpm test, pnpm test:browser locally.
• [X] I allow my PR to be updated by the reviewers (to speed up the review process).
• [X] I added unit tests.
• [ ] I added integration tests.
• [ ] I did not add automated tests because _____, and I am aware that a PR without tests will likely get rejected.

[nickreynolds]

@mirceanis there are a few places where documentation still needs to be updated, but wanted to get your thoughts on the refactor idea first