[IMP] bus: use 'pagehide' instead of 'unload' event

The original goal here is to remove the warning of the google page
speed but it actually is really better to use 'pagehide' as it is fired
more reliably than the 'unload' event and does not prevent Chrome and
Firefox to use the bfcache (browser optimization that enables instant
back and forward navigation).

The persisted property of the pagehide event is checked before
disconnecting from the worker. As for the presence/multi_tab case, it
was chosen to also consider page freezing as it seems more accurate that
what was done before (the main tab could be throttled/frozen which was
an issue).

Some resources to explain why this is better:
- https://web.dev/bfcache/#never-use-the-unload-event
- https://developer.mozilla.org/en-US/docs/Web/API/Window/pagehide_event



closes odoo/odoo#100976

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>