[FIX] mail: Unsychronize chat windows between mobile and desktop

Currently when you open, for example, 5 chat windows on the desktop,
each of those windows will be opened on mobile as well.
The big issue with that is that I have to shut down all windows before
starting to work on the application.

To make things simple, you have to explicitly open chat window to
make it appears on mobile. Synchronization is blocked in both direction.
We don't update the chat window state on the server and we no longer
consider notifications (bus) about it.

Tests were added in enterprise.

Task ID: 1891952

Backport of https://github.com/odoo/odoo/pull/41052



closes odoo/odoo#43546

Related: odoo/enterprise#7795
Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>