Make getNode function public

The getNode function should be public so that DomElement objects can be accessed directly if need be.
[Process] Added ProcessBuilder::addEnvironmentVariables
[Translation] Added support for JSON format (both loader and dumper).
Added doc comments
[DomCrawler] Added auto-discovery of namespaces in Crawler::filter() and Crawler::filterByXPath().

Improved content type guessing.
[DomCrawler] Made sure only the default namespace is removed when loading an XML content.
[DomCrawler] Added more tests for namespaced filtering.
[DomCrawler] Made that default namespace is no longer removed when loading documents with addXmlContent().
[DomCrawler] Added support for an automatic default namespace registration.
[DomCrawler] Updated the CHANGELOG with namespace auto-registration details.
[DomCrawler] Enabled default namespace prefix overloading.
[DomCrawler] Enabled manual namespace registration.
[HttpFoundation] Header `HTTP_X_FORWARDED_PROTO` can contain various values
Some proxies use `ssl` instead of `https`, as well as Lighttpd mod_proxy allows
value chaining (`https, http`, where `https` is always first when request is encrypted).
[HttpKernel] fix usage of deprecated FlattenException
Fixed an entity class name.

Broken in #7940.
merged branch jakzal/benchmark-tests-fix (PR #9117)

This PR was merged into the 2.2 branch.

Discussion
----------

Fixed an entity class name in a benchmark test

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

Broken in #7940 (67ba1314580ad63cbbf923b59157f226210d62ce). Since benchmark tests are not run on travis, it didn't complain.

Commits
-------

50ff35a Fixed an entity class name.
[DomCrawler] Removed checks if CssSelector is present.
[HttpFoundation] Remove useless reflection usage in MetadataBagTest
Update FormTypeCsrfExtension.php

There is no need to store the FormFactory in an Attribute.
The FormFactory can be retrieved directly.
Run all tests in parallel.