[13.x] Enhance error responses

[hafezdivandari]

This PR enhances error responses:

• More meaningful error responses to adhere OpenID specs for prompt=none ([11.x] Support disabling prompt when redirecting for authorization #1569):
  • login_required (ref)
  • consent_required (ref)
• Fix a bug on error responses of "implicit" grant. oauth2-server needs passing useFragment argument when generating redirect responses. Error parameters must be present on fragment instead of query parameters when redirecting to the client when using implicit grant.
• Add more feature tests for "authorization code" grant.
• Add feature tests for "authorization code" grant with PKCE.
• Add feature tests for "implicit" grant.