feat(DidDocument): keyType and Purpose-aware Verification Method helpers

[rmlearney-digicatapult]

Multiple points in the codebase use the same logic to resolve keys within a DID document

Created 2 self-describing helpers inside didDocument.ts for:

• findVerificationMethodsByPurpose()
• findVerificationMethodsByTypeAndPurpose()

Wired these helpers into call sites throughout the codebase to simplify reasoning:

• DQCL
• DidComm
• PEX
• Cheqd
• Webvh
• W3cJwt

Helpers necessary for fixing currently-broken linked-data-proofs when using Ed25519-2020 keys in subsequent PR

[changeset-bot]

🦋 Changeset detected

Latest commit: dd93927

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@credo-ts/core	Minor
@credo-ts/anoncreds	Minor
@credo-ts/cheqd	Minor
@credo-ts/didcomm	Minor
@credo-ts/webvh	Minor
@credo-ts/action-menu	Minor
@credo-ts/askar-to-drizzle-storage-migration	Minor
@credo-ts/askar	Minor
@credo-ts/drizzle-storage	Minor
@credo-ts/drpc	Minor
@credo-ts/hedera	Minor
@credo-ts/indy-vdr	Minor
@credo-ts/node	Minor
@credo-ts/openid4vc	Minor
@credo-ts/question-answer	Minor
@credo-ts/react-native	Minor
@credo-ts/redis-cache	Minor
@credo-ts/tenants	Minor

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