Add a formBuilder() method to ControllerBase

Updated: Comment #N

Problem/Motivation

Often one wants to have one or several forms as part of a rendered page. However, it's more work than it should be to inject the form_builder service into a _content controller class.

In addition, while \Drupal\Core\Controller\ControllerBase has a copy of the container, it's planned to make that private and currently is NOT supposed to be invoked directly like

$form_builder = $this->container()->get('form_builder');

Proposed resolution

Add a protected formBuilder() method to \Drupal\Core\Controller\ControllerBase similar to other methods that expose services.

Remaining tasks

Patch/test

User interface changes

N/A

API changes

Add a method to \Drupal\Core\Controller\ControllerBase