[FIX] website: show mega menu in + (extra) menu

The mega-menu inside "+" menu (that contains items that do not fit on
one line) could not be used at all.

This is because we only managed normal dropdown-menu (ul) and not
mega menu (div.o_mega_menu).

But once the menu is shown, there is an issue because the two main
widgets are column on "lg" breakpoint, and inside the menu there is no
width but we might still be on lg breakpoint.

So this commit also try to reset col values (max-width and flex) as is
the case in mobile view (because "col-lg" are not applied).

opw-2313019
closes #56367

closes odoo/odoo#56426

X-original-commit: 19de393288dec96c7151a58e8fafd70978d305e9
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

addons/website/static/src/scss/website.scss

@@ -670,7 +670,7 @@ $-transition-duration: 200ms;
             color: inherit; // Useful when the toggle is active
             pointer-events: none; // hack to prevent clicking on it because dropdown always opened
         }
-        > ul { // remove dropdown-menu default style as it is nested in another one
+        > ul, > .o_mega_menu { // remove dropdown-menu default style as it is nested in another one
             position: static;
             float: none;
             display: block;
@@ -680,6 +680,10 @@ $-transition-duration: 200ms;
             border: none;
             box-shadow: none;
         }
+        > .o_mega_menu .row > div { // remove mega menu col-lg-* style
+            max-width: none;
+            flex: auto;
+        }
     }
 }