[Form] fix form handling with unconventional request methods like OPTIONS
bug #12170 [Form] fix form handling with OPTIONS request method (Tobion)

This PR was merged into the 2.3 branch.

Discussion
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[Form] fix form handling with OPTIONS request method

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8282
| License       | MIT
| Doc PR        | -

The OPTIONS request is just handled as any other request method. And accoring to the spec, an options request can also contain a request body like a POST. This only applied when using the deprecated form processing with `$form->submit($request)`. The change also makes the handling consistent with the `handleRequest` behavior via https://github.com/symfony/symfony/blob/master/src/Symfony/Component/Form/Extension/HttpFoundation/HttpFoundationRequestHandler.php

Commits
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28eabd8 [Form] fix form handling with unconventional request methods like OPTIONS
Merge branch '2.3' into 2.5

* 2.3:
  added missing files
  [TwigBundle] added a test
  Indicate which file was being parsed if an exception is thrown while running translation:debug
  [ClassLoader] Cast $useIncludePath property to boolean
  [HttpFoundation] Minor spelling fix in PHPDocs
  improve error message for multiple documents
  [Session] remove invalid workaround in session regenerate
  [Kernel] ensure session is saved before sending response
  [Routing] serialize the compiled route to speed things up
  [Validator] Fixed Regex::getHtmlPattern() to work with complex and negated patterns
  [DependencyInjection] use inheritdoc for loaders
  [Config] fix filelocator with empty name
  [Form] fix form handling with unconventional request methods like OPTIONS
  CSRF warning docs on Request::enableHttpMethodParameterOverride()

Conflicts:
	src/Symfony/Component/Routing/Route.php