Allow nested markdown files for mailables (#41366)

Author: ahinkle

src/Illuminate/Foundation/Console/MailMakeCommand.php

@@ -102,7 +102,11 @@ protected function getView()
         $view = $this->option('markdown');
 
         if (! $view) {
-            $view = 'mail.'.Str::kebab(class_basename($this->argument('name')));
+            $name = str_replace('\\', '/', $this->argument('name'));
+
+            $view = 'mail.'.collect(explode('/', $name))
+                ->map(fn ($part) => Str::kebab($part))
+                ->implode('.');
         }
 
         return $view;