[IMP] base,web*: searchpanel in all multi record views

Before this rev. the searchpanel could only be activated in kanban
views (and it was specified in the kanban arch). From now on, the
searchpanel can be activated in any multi record view. It's arch
is moved to the search view arch (inside the <searchpanel> tag).

Task 1985921

Co-authored-by: Aaron Bohy <aab@odoo.com>