Solve https://github.com/PHP-DI/Slim-Bridge/issues/51

[solventt]

It fixes PHP-DI/Slim-Bridge#51

This package is a dependency of php-di/slim-bridge.

I remind that the php-di/Invoker breakes the PSR-15 middleware resolving in the Slim microframework. When one writes
$app->add(SomeMiddleware::class) it causes displaying NotCallableException.

To fix it - a couple of the code strings should be added (see below).

What was generally done in the pull-request code:

1) Adding the psr/http-server-middleware package to the require (composer.json) section to have MiddlewareInterface

2) Adding to the resolve method of the Invoker\CallableResolver class the following code:

if ($callable instanceof MiddlewareInterface) {
    return fn ($request, $next) => $callable->process($request, $next);
}

3) Adding a unit-test method checking middleware resolving

4) Adding four mock classes for the new test method: Middleware, Request, RequestHandler, Response

Also I want you to pay attention that the php-di/slim-bridge package has the performance problem: its dependency (this package) duplicates the routing code from the Slim\Routing\Route class. See detailed information - PHP-DI/Slim-Bridge#51 (comment)

[mnapoli]

Thank you

I don't think this might be the right approach since it introduces a special behavior for a PSR class. The Invoker tries to stay generic, we don't really want a if for a specific class in there.

I've merged another PR in Slim-bridge to fix the original issue.

[solventt]

@mnapoli There is a big problem - AdvancedCallableResolver will be removed in Slim 5 (see issue). So the merge you have done will soon become obsolete.