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
Return BC compatibility for `@Route` parameters and default values
[FrameworkBundle] The config:dump-reference command shows the list of bundles with the table helper
[Serializer] Added XML attributes support for DomDocument in XmlEncoder.

This is a combination of 2 commits.

- [Serializer] Added encoding support for DomDocument in XmlEncoder

- [Serializer] Refactor code to allow setting <?xml standalone ?>

This commit refactors the createDomDocument(..) method in XmlEncoder
so
it can set the 'version', 'encoding' and 'standalone' attributes on
the
DOM document.

Code coverage of new code: 100%. Tests: pass.
Ignore null value in comparison validators
[Validator] fixed StaticMethodLoader trying to invoke methods of abstract classes (closes #8589)
removed dead code and fixed CS
merged branch fabpot/validator-abstract-fix (PR #8592)

This PR was merged into the 2.2 branch.

Discussion
----------

[Validator] Fixed StaticMethodLoader does not try to invoke methods of abstract classes anymore

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8589
| License       | MIT
| Doc PR        |  n/a

Commits
-------

b41cf82 [Validator] fixed StaticMethodLoader trying to invoke methods of abstract classes (closes #8589)
merged branch fabpot/dead-code (PR #8572)

This PR was merged into the 2.2 branch.

Discussion
----------

removed dead code and fixed CS

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

Commits
-------

7d58147 removed dead code and fixed CS
merged branch fabpot/console-fix (PR #8600)

This PR was merged into the 2.3 branch.

Discussion
----------

[FrameworkBundle] fixed regression where the command might have the wrong container if the application is reused several times

Commits
-------

1bd45b3 [FrameworkBundle] fixed regression where the command might have the wrong container if the application is reused several times
[routing] added ability for apache matcher to handle array values
[HttpFoundation] deprecated FlashBag::getIterator() method
[WebProfilerBundle] made toolbar listener instantiation conditional
[Console] fixed tests
Revert "[Form] Remove "value" attribute on empty_value option"

This reverts commit 9e849eb78bcc668a2b8aad39cb47e2ad32c73a47.

Reasons for the revert:

* https://github.com/symfony/symfony/issues/8478
* https://github.com/symfony/symfony/issues/8526
[Form] Removed the "disabled" attribute from the placeholder option in select fields due to problems with the BlackBerry 10 browser
Fixes link indices
[Form] Changed (Number|Integer)ToLocalizedStringTransformer::reverseTransform() to do rounding
[Form] Fixed: If a form is not present in a request, it is not automatically submitted