[9.x] Make Illuminate\Mail\Mailable macroable (#40631)

This PR makes the \Illuminate\Mail\Mailable class macroable. A simple use-case is abstracting the options array when having multiple Mailables that you want to attach raw pdf data to:

```php
// Current:

Mail::send((new MyMail())->attachData($pdfData, 'filename.pdf', [
    'mime' => 'application/pdf',
]));

// Proposal:

Mailable::macro('attachPdfData', function ($data, $name) {
    return $this->attachData($data, $name, [
        'mime' => 'application/pdf',
    ]);
});

Mail::send((new MyMail())->attachPdfData($pdfData, 'filename.pdf'));
```

Author: mweghorst

src/Illuminate/Mail/Mailable.php

@@ -15,14 +15,17 @@
 use Illuminate\Support\Traits\Conditionable;
 use Illuminate\Support\Traits\ForwardsCalls;
 use Illuminate\Support\Traits\Localizable;
+use Illuminate\Support\Traits\Macroable;
 use Illuminate\Testing\Constraints\SeeInOrder;
 use PHPUnit\Framework\Assert as PHPUnit;
 use ReflectionClass;
 use ReflectionProperty;
 
 class Mailable implements MailableContract, Renderable
 {
-    use Conditionable, ForwardsCalls, Localizable;
+    use Conditionable, ForwardsCalls, Localizable, Macroable {
+        __call as macroCall;
+    }
 
     /**
      * The locale of the message.
@@ -1053,6 +1056,10 @@ public static function buildViewDataUsing(callable $callback)
      */
     public function __call($method, $parameters)
     {
+        if (static::hasMacro($method)) {
+            return $this->macroCall($method, $parameters);
+        }
+
         if (Str::startsWith($method, 'with')) {
             return $this->with(Str::camel(substr($method, 4)), $parameters[0]);
         }