Add "synthetic"/ "mock" FIDO2 credential creation.

[JMarkstrom]

Add support for synthetic (mock) FIDO2 credential creation

Add support for “synthetic” (locally generated) FIDO2 credential creation and rename FakeChallange to CreateSyntheticChallenge.

Introduce a Synthetic parameter set on New-YubiKeyFIDO2Credential that:

• Generates challenge, user ID, and user entity locally
• Requires only -RelyingPartyID and -Username
• Eliminates the need for an external IdP

Goal: Enable standalone FIDO2 credential creation and simplify workflows for large blob and PRT scenarios by allowing credentials to be created on demand.

Details

• Challenge.cs: Add CreateSyntheticChallenge (32 random bytes); deprecate FakeChallange as an [Obsolete] wrapper for backward compatibility
• SyntheticCredentialHelper.cs (new): GenerateUserID returns 32 cryptographically secure random bytes for WebAuthn user.id
• NewFIDO2Credential.cs:
  • Add Synthetic parameter set
  • Default UserDisplayName to Username
  • Populate synthetic values in ProcessRecord
  • Add “Touch the YubiKey…” prompt and WriteInformation confirmation
  • Update XML documentation and examples
• CredentialData.cs: Add PublicKey and CredentialId convenience properties
• 310-FIDO2.tests.ps1: Add Pester tests for the synthetic parameter set