…lexandre, javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Add the `_failure_path` hidden field in template

Today I learnt about this [feature](symfony/symfony@d0057d0) so I guess it was time to document it.

Basically, what we can do with the `_target_path` form field is also possible for failure via the `_failure_path` field. It's very useful when you want multiple login forms for the same firewall (a general login, and a login during e-commerce checkout for example).

I also moved the sections to me more logic, as the last section was about **Redirecting on Login Failure** via the option - because it was not explained yet in the page. This section is now just before the updated **Control the Redirect URL from inside the Form**.

Commits
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a865da1 Use different values for target_path_parameter and failure_path_parameter
1fc80af Minor rewords
93cf9bd Add the `_failure_path` hidden field in template

* 2.7:
  [#7620] use generate() in PHP templates before 2.8

* 2.8: (46 commits)
  [#7507] fix component name
  [#7490] minor typo fix
  Added a note about redirections to absolute URLs in tests
  Added the changes suggested by reviewers
  [#7620] use generate() in PHP templates before 2.8
  Fixed the RST syntax
  Improve example context
  [#5621] Enhancing example of using bundle config
  [#7601] minor tweak
  Update expiration.rst
  Update expiration.rst
  Update expiration.rst
  Update expiration.rst
  Minor reword and fixed the line length
  Improve specification explanation
  [#7664] minor wording tweak
  Rewords and minor fixes
  Add an explanation about «constraints» validation
  [#7645] enumerate ordered list items implicitly
  Adding a new article about "Creating a Bug Reproducer"
  ...

* 3.2: (71 commits)
  Rewriting the service container docs
  Minor reword
  Adding a tip for validation in forms without class
  [#7217] add versionadded directives
  [#7203] merge note and versionadded directive
  Use the new configurator YAML syntax
  Added a note about the .htaccess files included by Symfony apps
  Made unmapped field example in forms chapter more descriptive
  [#7507] fix namespace
  [#7507] fix component name
  [#7490] minor typo fix
  Added a note about redirections to absolute URLs in tests
  [#7204] link to API doc
  Added docs for JsonResponse::fromJsonString
  Added the changes suggested by reviewers
  [#7620] use generate() in PHP templates before 2.8
  Fixed the RST syntax
  Improve example context
  Minor formatting changes
  [#7519] some minor tweaks
  ...