…eu88160)

This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes #7560).

Discussion
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Resolving $this usage outside a class on form.rst

This commit take care of the framework use code examples only.

The "Creating a simple Form" define the coding place to be into a controller action method. Unlikely, the documentation consider into the other examples that the reader will know the place of the sample code. This does not allow the examples to be standalone and can lead some disappointment for which one want to have informations about a single section.

This commit offer to place the code samples into the default controller to create a logic use of the "$this" special variable.

Commits
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8cf9cd2 Resolving $this usage outside a class on form.rst

* 2.7: (30 commits)
  [#7560] remove unused use statements
  Resolving $this usage outside a class on form.rst
  Fix some odd English in the PDOSessionHandler docs
  Fix typo
  Add the description for the HTTP status because it's not that common
  Update exception code status
  [#7592] some minor tweaks
  Fix link for Twig Extensions documentation
  Update framework.rst [Fix esi tag]
  Update render_without_controller.rst
  Update matchers.rst
  Update matchers.rst
  Update locale_sticky_session.rst
  Update framework.rst
  Update import.rst
  Update load_balancer_reverse_proxy.rst
  Moved the requirements file
  [#7509] add missing references
  Added a mention to APCu Polyfill in the performance article
  [#7497] minor rewording
  ...