[FIX] mail: hide email preview when replying on Outlook desktop client

Steps to reproduce:

  - Go to any contact
  - Send message to this contact (in the chatter) with text "test"
  - Open the email with Outlook desktop client on Windows
  - Reply to the mail (or transfer it)

Issue:

  The email preview is displayed in top of the mail;
  `test` is displayed twice.

Cause:

  Outlook desktop client does not handle well the `display:none`.

Solution:

  Set font color to white and set a minimum font size and line height;
  the text will still be present, but not noticeable.

opw-3167169

closes odoo/odoo#118440

X-original-commit: 8bcd8186ffb67c1abb57f9316dbbc616ba343e0a
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mail/data/mail_templates_email_layouts.xml

@@ -180,7 +180,7 @@
         </template>
 
         <template id="notification_preview">
-<div style="display: none; max-height: 0px; overflow: hidden;">
+<div style="display: none; max-height: 0px; overflow: hidden; color:#fff; font-size:0px; line-height:0px">
     <t t-if="tracking_values">
         <t t-out="tracking_values[0][0]"/>: <t t-out="tracking_values[0][1]"/> &#8594; <t t-out="tracking_values[0][2]"/>
         <t t-if="len(tracking_values) > 1"> |...</t>