## Impacted versions:
 8.0 / 9.0 / 10.0
## Steps to reproduce:
* see https://github.com/odoo/odoo/issues/11841
* in a shell
  1. create an in memory record `order = self.env['purcahse.order'].new({....})`
  2. create an in memory record with a reference to the first one `order_line = self.env['purchase.order.line'].new({'order_id': order, ....})`
  3. order_line.order_id is an in memory recordset
  4. create a record for a model that inherits from mail.thread `self.env['product.product'].create({....})`
  5. At this stage order_line.order_id is an empty recordset

## Current behavior:
 In memory records are dropped when a call is done to self.invalidate_cache
## Expected behavior:
In memory records are preserved when a call is done to self.invalidate_cache


There are lot of places where the method `invalidate_cache` is called and the silent removal of the in memory records from all environments has unpredictable effects on fields modified by a computed method or an onchange or even related fields .... Moreover since all caches are invalidated each time you create / write / unlink  (https://github.com/odoo/odoo/blob/10.0/addons/mail/models/mail_followers.py#L111) an instance of a model that inherits from 'mail.thread', the performances of the server are severely penalized.

OPW703903

message = self.pool['mail.message'].browse(cr, SUPERUSER_ID, message_id, context=context)
        
        email_pids = self.get_partners_to_email(cr, uid, ids, message, context=context)
        if not email_pids:
            return True
        
        body_html = message.body
        
        user_id = message.author_id and message.author_id.user_ids and message.author_id.user_ids[0] and message.author_id.user_ids[0].id or None
        signature_company = self.get_signature_footer(cr, uid, user_id, res_model=message.model, res_id=message.res_id, context=context, user_signature=(user_signature and message.model != 'mail.group'))
        if signature_company:
            body_html = tools.append_content_to_html(body_html, signature_company, plaintext=False, container_tag='div')
        
        references = message.parent_id.message_id if message.parent_id else False
        
        custom_values = dict()
        if message.model and message.res_id and self.pool.get(message.model) and hasattr(self.pool[message.model], 'message_get_email_values'):
            custom_values = self.pool[message.model].message_get_email_values(cr, uid, message.res_id, message, context=context)