Add Bearer Token Test Support

[jzheaux]

Related to #6634

Testing authentication flows that include a JWT is straight-forward:

this.mvc.perform(get("/")
    .with(jwt(jwt -> jwt.subject("subject"))));

It'd be nice to have Resource Server support that doesn't care about the format"

this.mvc.perform(get("/")
    .with(bearer(b -> b.subject("subject"))));

While the first produces a JwtAuthenticationToken and Jwt principal, the second would produce a BearerTokenAuthentication and a OAuth2AuthenticatedPrincipal principal.