[IMP] website: floating dropdown of search bar

Prior to this commit, the dropdown of the search bar which was displayed
in a navbar had a static position when the viewport was below lg.
This dropdown pushed the navigation down instead of being in front of
it, creating a layout issue in the offcanvas menu.

To fix this, this commit forces the `dropdown_menu` of the search bar to
be in absolute position.

task-3060986

Part-of: odoo/odoo#119650

addons/website/static/src/snippets/s_searchbar/000.xml

@@ -3,7 +3,7 @@
 
 <!-- Search Bar autocomplete item -->
 <div t-name="website.s_searchbar.autocomplete"
-    class="o_dropdown_menu show w-100">
+    class="o_dropdown_menu show position-absolute w-100">
     <t t-if="fuzzySearch and results.length">
         <span class="dropdown-item-text">
             <span class="text-muted">No results found for '<t t-esc="search"/>'. Showing results for '<a href="#" class="s_searchbar_fuzzy_submit" t-esc="fuzzySearch"/>'.</span>