PSR-7 & PSR-15 support for WordPress Routes

[broskees]

This PR add PSR-7 & PSR-15 support for WordPress Routes.

By using output buffering to capture WordPress's output and make it the body of a Response, we can force WordPress requests to actually emit a Response class. This allows PSR-15 (Middleware) and and PSR-7 (Request/Response classes) compatibility for WordPress itself. This works EVEN if WordPress uses output buffering as well, since output buffering can handle nested calls (see here).

WordPress requests are already a Laravel Route, why is this necessary also?

For Middleware to be fully functional, they should also be able to make changes to the Response before it's sent to the client (See Laravel's documentation for an example of this: https://laravel.com/docs/10.x/middleware#before-after-middleware). This is impossible unless there is an actual Response class to manipulate.

Additionally, I'm improving on my last PR by using named routes instead of using a fake JsonResponse to identify WordPress requests like in my last PR. This lowers our maintenance burden and uses Laravel's native route matching to identify WordPress routes instead.

[QWp6t]

@Log1x, @broskees

Does my refactor make sense to y'all? If so, we can merge this. (I just didn't want to do a significant refactor without another pair of eyes peepin' it.)

[Log1x]

Does my refactor make sense to y'all? If so, we can merge this. (I just didn't want to do a significant refactor without another pair of eyes peepin' it.)

LGTM