Add RegistersRouteFiles trait to ServiceProvider

[garanaibrahim7]

What this PR does

Adds a RegistersRouteFiles trait to ServiceProvider that provides
a fluent, cache-compatible API for loading route files without manual
require calls or repetitive Route::group() boilerplate.

Usage

$this->registerRouteFiles('api');
$this->registerRouteFiles(['web', 'api', 'admin']);
$this->registerRouteFiles('api/v2', [
'middleware' => ['api', 'auth:sanctum'],
'prefix' => 'api/v2',
]);

Why

• No bare require — fully compatible with php artisan route:cache
• Deduplication across multiple ServiceProviders
• Resolves relative and absolute paths automatically
• Fluent chaining supported

[rodrigopedra]

So instead of calling:

$router->middleware(['api', 'auth:sanctum'])
    ->prefix('/api')
    ->as('api.')
    ->group($app->basePath('routes/api.php'));

Your proposal is this would be more "fluent" or straightforward?

$router->registerRouteFiles('api', [
    'middleware' => ['api', 'auth:sanctum'],
    'prefix' => '/api',
    'as' => 'api.',
]);

Are there any other benefits that would counter the loss of IDE autocompletion, for example?

Mind that $app and $router are passed down when configuring routing with a closure on bootstrap/app.php:

<?php

use Illuminate\Foundation\Application;
use Illuminate\Foundation\Configuration\Exceptions;
use Illuminate\Foundation\Configuration\Middleware;
use Illuminate\Routing\Router;

return Application::configure(basePath: dirname(__DIR__))
    ->withRouting(function (Application $app, Router $router) {
        $router->middleware(['api', 'auth:sanctum'])
            ->prefix('/api')
            ->as('api.')
            ->group($app->basePath('routes/api.php'));

        $router->middleware('web')
            ->group($app->basePath('routes/web.php'));
    })
    ->withCommands([dirname(__DIR__) . '/routes/console.php'])
    ->withMiddleware(function (Middleware $middleware): void {
        //
    })
    ->withExceptions(function (Exceptions $exceptions): void {
        //
    })->create();