refactor: use struct types for claim related types

BREAKING change.
The following types are changed from interface to struct type:

- AccessTokenClaims
- IDTokenClaims
- IntrospectionResponse
- UserInfo and related types.

The following methods of OPStorage now take a pointer to a struct type,
instead of an interface:

- SetUserinfoFromScopes
- SetUserinfoFromToken
- SetIntrospectionFromToken

The following functions are now generic, so that type-safe extension
of Claims is now possible:

- op.VerifyIDTokenHint
- op.VerifyAccessToken
- rp.VerifyTokens
- rp.VerifyIDToken

pkg/client/client.go

@@ -176,8 +176,8 @@ func SignedJWTProfileAssertion(clientID string, audience []string, expiration ti
 		Issuer:    clientID,
 		Subject:   clientID,
 		Audience:  audience,
-		ExpiresAt: oidc.Time(exp),
-		IssuedAt:  oidc.Time(iat),
+		ExpiresAt: oidc.FromTime(exp),
+		IssuedAt:  oidc.FromTime(iat),
 	}, signer)
 }