[8.x] Unified asset publishing (#5654)

* [8.x] Unified asset publishing

* Update composer.json

Co-authored-by: Taylor Otwell <taylor@laravel.com>

composer.json

@@ -37,6 +37,9 @@
             "Illuminate\\Foundation\\ComposerScripts::postAutoloadDump",
             "@php artisan package:discover --ansi"
         ],
+        "post-update-cmd": [
+            "@php artisan vendor:publish --tag=laravel-assets --ansi"
+        ],
         "post-root-package-install": [
             "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
         ],