Add console extender (#2057)

* Made the console command system extender-friendly

* Added console extender

* Added ConsoleTestCase to integration tests

* Added integration tests for console extender

* Marked event-based console extension system as deprecated

* Moved trimming command output of whitespace into superclass

* Renamed 'add' to 'command'

* Added special processing for laravel commands

* Code style fixes

* More style fixes

* Fixed $this->container

tests/integration/extenders/ConsoleTest.php

@@ -0,0 +1,65 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration\extenders;
+
+use Flarum\Console\AbstractCommand;
+use Flarum\Extend;
+use Flarum\Tests\integration\ConsoleTestCase;
+
+class ConsoleTest extends ConsoleTestCase
+{
+    /**
+     * @test
+     */
+    public function custom_command_doesnt_exist_by_default()
+    {
+        $input = [
+            'command' => 'customTestCommand'
+        ];
+
+        $this->assertEquals('Command "customTestCommand" is not defined.', $this->runCommand($input));
+    }
+
+    /**
+     * @test
+     */
+    public function custom_command_exists_when_added()
+    {
+        $this->extend(
+            (new Extend\Console())
+                ->command(CustomCommand::class)
+        );
+
+        $input = [
+            'command' => 'customTestCommand'
+        ];
+
+        $this->assertEquals('Custom Command.', $this->runCommand($input));
+    }
+}
+
+class CustomCommand extends AbstractCommand
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected function configure()
+    {
+        $this->setName('customTestCommand');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function fire()
+    {
+        $this->info('Custom Command.');
+    }
+}