SkinMustache in core provides most of what is required for Vector to
generate its menus. In the interest of having a canonical source of
truth for menus across all skins, Vector should use this data.
To ensure the HTML generated is (mostly) the same after this patch to
prior, a few modifications are necessary:
* The data from core is decorated so that Vector can continue having its
own custom class names on menus. This is done using the
decoratePortletClass method.
* There is no support for a menu having a header representing the
selected menu item, as is currently the case with variants. This is
achieved via an extension to getPortletData. It's assumed that later
when variants are merged with languages, this can be removed.
* Menus are agnostic to how they are displayed, so we must continue to
add the is-dropdown template variable to drop down menus. In future we
may want to rethink our Menu partial to make this unnecessary in PHP.
* The portal-first class is redundant in the modern Vector as we can
use the first-child selector. Previously we introduced a class to
service the legacy skin where this rule doesn't apply as #p-logo is
the first child. However, the legacy skin can do this using a special
next sibling selector instead.
Bug: T268157
Change-Id: I5f7adc1840441b508ffee40139b85b64021789e6
9f1a1fa829