[5.4] Allow routes to be registered fluently

[JosephSilber]

This enables stuff like:

Route::name('users.index')->middleware('auth')->get('users', function () {
    // some closure action...
});

...so that the calls to name and middleware are not hanging off the end of the closure.

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Also, you can now use the middleware method with groups:

Route::middleware('auth')->prefix('api')->group(function () {
    // register some routes...
});

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Finally, you can now register middleware for resources directly:

Route::middleware('auth')->resource('photo', 'PhotoController');

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P.S. This has been previously attempted in #14354. Taking another stab at it here after talking it through with Taylor.