feat: Add support for inline attachments (#56598)

Author: jayanratna

src/Illuminate/Mail/Transport/ResendTransport.php

@@ -73,7 +73,7 @@ protected function doSend(SentMessage $message): void
             foreach ($email->getAttachments() as $attachment) {
                 $attachmentHeaders = $attachment->getPreparedHeaders();
                 $contentType = $attachmentHeaders->get('Content-Type')->getBody();
-
+                $disposition = $attachmentHeaders->getHeaderBody('Content-Disposition');
                 $filename = $attachmentHeaders->getHeaderParameter('Content-Disposition', 'filename');
 
                 if ($contentType == 'text/calendar') {
@@ -88,6 +88,10 @@ protected function doSend(SentMessage $message): void
                     'filename' => $filename,
                 ];
 
+                if ($disposition === 'inline') {
+                    $item['inline_content_id'] = $attachment->hasContentId() ? $attachment->getContentId() : $filename;
+                }
+
                 $attachments[] = $item;
             }
         }