Theme hook suggestion for node view mode added

Previously node template suggestions were only based on the nodes' bundle and their id. It was very common to add manually new suggestions based on the view modes manually by themers to get a more flexible template architecture. So these template suggestions have been added to core.

Previously, in D7 and D8 before the patch:

<!-- THEME DEBUG -->
<!-- CALL: _theme('node') -->
<!-- FILE NAME SUGGESTIONS:
   * node--1.html.twig
   * node--article.html.twig
   x node.html.twig
-->
<!-- BEGIN OUTPUT from 'core/themes/bartik/templates/node.html.twig' -->

D8 after the change:

<!-- THEME DEBUG -->
<!-- CALL: _theme('node') -->
<!-- FILE NAME SUGGESTIONS:
   * node--1--full.html.twig
   * node--1.html.twig
   * node--article--full.html.twig
   * node--article.html.twig
   * node--full.html.twig
   x node.html.twig
-->
<!-- BEGIN OUTPUT from 'core/themes/bartik/templates/node.html.twig' -->

This change adds new feature required by a huge number of developers and themers out of the box.