Fixes #737: Twig validation does not recognize Drupal filters/functions.

[grasmash]

No description provided.

[grasmash]

Unfortunately, we've got to downgrade this feature to a degree. We're switching to pure syntax checking and ignoring things like filter/function checks.

The previous approach required a real compilation of twig into php, which would have required a full Drupal bootstrap and real implementation of Drupal core's twig extension. That was just a bit too much of a rabbit hole for me to chase.

However, this could be a good feature for Drupal Console, which is container aware. @jmolivas you might be interested in adding twig validation.

[grasmash]

If you wanted to go all the way here, you'd actually add Drupal core's Twig extension:

$twig = new \Twig_Environment(NULL, array(
  'debug' => TRUE,
  'cache' => FALSE,
  'autoescape' => 'html',
  'optimizations' => 0
));
$twig->addExtension(new TwigExtension($renderer);

You need a real Drupal container to instantiate $renderer.