[FIX] mail, various: remove outdated "render_safe" rendering option

Render safe option was used with Jinja rendering to tell Jinja that content
was safe and was not expected to be escaped. This was used notably in subject
as characters like ``&`` was escaped in email subject (e.g. `R&D News`).

This is now supported directly by the "inline template" rendering engine that
is used to render text-based templates since Odoo v15 [1]. This option is not
supported by code anymore anyway and leads to nothing.

Task-2088884 (MailComposer: Onchange to editable computed stored)
Task-2710804 (MailThread Api Cleaning)

[1] See odoo/odoo@68182baff4

Prepares Task-2088884 (Mail: Composer Onchange to Editable Computed Stored)

Part-of: odoo/odoo#94660

addons/mail/models/mail_template.py

@@ -193,7 +193,6 @@ class MailTemplate(models.Model):
             for field in fields:
                 generated_field_values = template._render_field(
                     field, template_res_ids,
-                    options={'render_safe': field == 'subject'},
                     post_process=(field == 'body_html')
                 )
                 for res_id, field_value in generated_field_values.items():

addons/mail/wizard/mail_compose_message.py

@@ -602,7 +602,7 @@ class MailComposer(models.TransientModel):
             multi_mode = False
             res_ids = [res_ids]
 
-        subjects = self._render_field('subject', res_ids, options={"render_safe": True})
+        subjects = self._render_field('subject', res_ids)
         # We want to preserve comments in emails so as to keep mso conditionals
         bodies = self._render_field('body', res_ids, post_process=True, options={'preserve_comments': self.composition_mode == 'mass_mail'})
         emails_from = self._render_field('email_from', res_ids)

addons/survey/wizard/survey_invite.py

@@ -210,7 +210,7 @@ class SurveyInvite(models.TransientModel):
 
     def _send_mail(self, answer):
         """ Create mail specific for recipient containing notably its access token """
-        subject = self._render_field('subject', answer.ids, options={'render_safe': True})[answer.id]
+        subject = self._render_field('subject', answer.ids)[answer.id]
         body = self._render_field('body', answer.ids, post_process=True)[answer.id]
         # post the message
         mail_values = {

addons/website_slides/wizard/slide_channel_invite.py

@@ -66,7 +66,7 @@ class SlideChannelInvite(models.TransientModel):
 
     def _prepare_mail_values(self, slide_channel_partner):
         """ Create mail specific for recipient """
-        subject = self._render_field('subject', slide_channel_partner.ids, options={'render_safe': True})[slide_channel_partner.id]
+        subject = self._render_field('subject', slide_channel_partner.ids)[slide_channel_partner.id]
         body = self._render_field('body', slide_channel_partner.ids, post_process=True)[slide_channel_partner.id]
         # post the message
         mail_values = {