[FIX] web_editor: restore background videos (new imagepicker UI)

Commit [1] broke the background videos feature. This is because the
'we-imagepicker' widget is now a sub-widget of a new 'we-button-group'
widget, acting as a selection choice (same as we-button in a we-select).
When selecting a selection choice, the appropriate option method is
called, with the selection value and params... but the params were
actually the ones of the 'we-button-group' element and not the ones
of the chosen widget 'we-imagepicker'.

This has never been important for we-select widgets but it could have
been. The problem is only solved here in master, generically for all
selection widgets (currently only 'we-select' and 'we-button-group').
The params received are the ones of the active sub-widget combined with
the ones of the selection widget.

[1]: https://github.com/odoo/odoo/commit/bb0cd4d5c82a9c2311f8c45ced0e9fdc0397d292



closes odoo/odoo#54629

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