Select and order columns should be instantly resolved

Currently a call to Query::with() is mandatory (see https://github.com/Icinga/ipl-orm/commit/7dc53f1e4a4214444dd575e3c58c3f777cc6e34b) in order to be able to differentiate a column from being solely used in a filter or from being selected.

Consider the following:

$query = Service::on($this->getDb());

$query->with('service.vars');
$query->columns('service.vars.flatvalue');
$query->where('service.vars.flatname', 'app');

The call to with() here shouldn't be necessary, the call to columns should do so instantly. Instantly because with() does the same and it is required for any filter optimizations to work correctly.

At the moment relations of selected columns are only resolved in Query::assembleSelect(). This is too late and can't be assumed as an requirement for e.g. filter optimizations.

Start by reading Query::with(), Query::columns(), and Query::assembleSelect() to trace when selected-column relations are resolved and how filter optimizations use them. Done means selecting service.vars.flatvalue through columns() resolves the relation immediately, so the explicit with() call is unnecessary while filter optimizations continue to work correctly.