[2.0.0-beta1] Resolve Twig namespaces in _template property

Is activating the component module enough?

Maybe we will remove _template all together.
Let's wait and discuss.

If we remove this property, don't forget to:

• Revert this change : 🐛 [2.0.0-alpha2] Wrong template name leads to Deprecated: basename(): Passing null to parameter #1 ($path) Fixed
• Update the specification
• Close the SDC issue: ✨ Allow declaration of template path in SDC Active

Finally, we keep it.