AuthenticationPrincipalArgumentResolver should use BeanResolver

[rwinch]

AuthenticationPrincipalArgumentResolver should use BeanResolver. This will allow the @AuthenticationPrincipal to refer to a @Bean. This would allow something like:

@AuthenticationPrincipal("@jpaEntityManager.merge(#this)")
public String doStuff(MyUserEntity currentUser) {
    currentUser.setProperty(...);
    // MyUserEntity is attached and will be merged
    ...
}