[FIX] mail: create attachments with the correct filename when using the popup editor

Send a message using the popup editor.
Drag and drop an image into the message content.
It will create an attachment for the inlined image.
To generate the values for the attachment, a regex is used to parse the content.
Besides summoning Eldritch abominations, it didnt't take into account the
original filename, whereas the default one (image) would have no extension.
We extend the regex to capture the filename and use it.

opw 1903194

closes odoo/odoo#28527

addons/mail/models/mail_message.py

@@ -12,7 +12,7 @@ from odoo.exceptions import UserError, AccessError
 from odoo.osv import expression
 
 _logger = logging.getLogger(__name__)
-_image_dataurl = re.compile(r'(data:image/[a-z]+?);base64,([a-z0-9+/\n]{3,}=*)\n*([\'"])', re.I)
+_image_dataurl = re.compile(r'(data:image/[a-z]+?);base64,([a-z0-9+/\n]{3,}=*)\n*([\'"])(?: data-filename="([^"]*)")?', re.I)
 
 
 class Message(models.Model):
@@ -762,7 +762,7 @@ class Message(models.Model):
             def base64_to_boundary(match):
                 key = match.group(2)
                 if not data_to_url.get(key):
-                    name = 'image%s' % len(data_to_url)
+                    name = match.group(4) if match.group(4) else 'image%s' % len(data_to_url)
                     attachment = Attachments.create({
                         'name': name,
                         'datas': match.group(2),