Pass Eslint validations: Form API example [#3417502]

Problem/Motivation

At #3417482: [Meta] Pass Eslint validations we are aiming to have all the eslint validation checks passing for the Examples module.

On this issue, we'll be focused on the form_api_example sub-module

Initial errors detected by 27/01/2024

/modules/form_api_example/form_api_example.routing.yml
  16:17  error  Multiple spaces found before ''\Drupal\form_api_example\Controller\Page::description''  no-multi-spaces
  24:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\SimpleForm''               no-multi-spaces
  32:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\InputDemo''                no-multi-spaces
  40:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\StateDemo''                no-multi-spaces
  48:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\ContainerDemo''            no-multi-spaces
  56:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\VerticalTabsDemo''         no-multi-spaces
  64:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\ModalForm''                no-multi-spaces
  73:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\AjaxColorForm''            no-multi-spaces
  81:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\BuildDemo''                no-multi-spaces
  89:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\AjaxAddMore''              no-multi-spaces
  97:11  error  Multiple spaces found before ''\Drupal\form_api_example\Form\AjaxAddRemoveElements''    no-multi-spaces

Proposed resolution

Check the parent issue for detailed instructions about how to run eslint locally
Run eslint against the submodule: form_api_example
Fix the issues found and make a MR with the fixes.