Unable to generateTokens with correct body when using a CookielessRequestInit resource

[cgooding-va]

In generateTokens, when a string resource is specified, it will build a body for the request here that includes the private _cookielessApiToken and _cookielessNavigationToken tokens.

However, if a CookielessRequestInit resource is used instead (as I wish to do as I would like to include an Authorization header on my request), these tokens are not injected into the body. There's no real way to inject them myself as they are currently private and I have to build the request during the embed init anyways.