[FIX] web: avoid long menu dropdown overflow

The Actions/Print dropdowns may overflow the screen in case of very long
lists of menu entries, when based solely on the default BS4 styles for
`dropdown-menu`.

The `o_dropdown_menu` class forces a vertical limit and a scrollbar when
this happens, and should be applied to those control-panel dropdowns to
prevent this UI glitch.

See also 1c1c0897e8 which adapted
dropdowns to BS4.

closes odoo/odoo#31251

addons/web/static/src/xml/base.xml

@@ -341,7 +341,7 @@
                     <t t-raw="item.label"/>
                 </a>
             </t>
-            <div class="dropdown-menu" role="menu">
+            <div class="dropdown-menu o_dropdown_menu" role="menu">
                 <t t-foreach="widget.items[section.name]" t-as="item">
                     <t t-if="section.name == 'files'">
                         <t t-set="item.title">