[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.
[Twig] fixed TwigEngine::exists() method when a template contains a syntax error (closes #88546)
merged branch fabpot/twig-engine-exists (PR #8547)

This PR was merged into the 2.2 branch.

Discussion
----------

[Twig] fixed TwigEngine::exists() method when a template contains a syntax error (closes #8546)

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8546
| License       | MIT
| Doc PR        | n/a

Commits
-------

ae7fa11 [Twig] fixed TwigEngine::exists() method when a template contains a syntax error (closes #88546)
Developer friendly Class Not Found and Undefined Function errors.
[Debug] fixed CS
[Debug] made guessing of possible class names more flexible
[Debug] made Debug find FQCN automatically based on well-known autoloaders
[Debug] moved special fatal error handlers to their own classes
[Debug] refactored unit tests
[Tests] Tests on php 5.5 should pass

Because php 5.5 is stable now
merged branch lyrixx/php55 (PR #8559)

This PR was merged into the 2.2 branch.

Discussion
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[Tests] Tests on php 5.5 should pass

Because php 5.5 is stable now

Commits
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0086ee3 [Tests] Tests on php 5.5 should pass
The ignoreAttributes itself should be ignored, too.
merged branch derrabus/ignore_attributes_in_redirect_controller (PR #8563)

This PR was merged into the 2.3 branch.

Discussion
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[FrameworkBundle] RedirectCotroller: The ignoreAttributes parameter should be ignored

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

As discussed in PR #7590, when pointing a route to FrameworkBundle's `RedirectController` the attribute `ignoreAttributes` is added to the new route's attributes, if specified as array. As @lsmith77 wrote in a comment to that PR, this should not be the intended behavior. A valid workaround is to add `ignoreAttributes` itself to this array.

The problem remained undiscovered by the unit test, as `ignoreAttribues` was not included in the `_route_params` of the faked `Request` object. This PR should fix both, the unit test and the `RedirectController` itself, so the workaround mentioned above is not necessary anymore. Additionally, my fix should not break any routing configuration that is using the workaround.

Commits
-------

dc1fff0 The ignoreAttributes itself should be ignored, too.
fixed file permission
[DependencyInjection] fixed #8570
[DependencyInjection] fixed regression where setting a service to null did not trigger a re-creation of the service when getting it
merged branch fabpot/null-services (PR #8582)

This PR was merged into the 2.3 branch.

Discussion
----------

[DependencyInjection] fixed regression where setting a service to null did not trigger a re-creation of the service when getting it (closes #8392)

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8392
| License       | MIT
| Doc PR        | n/a

Commits
-------

50d0727 [DependencyInjection] fixed regression where setting a service to null did not trigger a re-creation of the service when getting it
merged branch bronze1man/PR-setLazy-parent-2.3 (PR #8573)

This PR was merged into the 2.3 branch.

Discussion
----------

[DependencyInjection] setLazy not work on DefinitionDecorator

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8570
| License       | MIT
| Doc PR        | n/a

Commits
-------

970ce2c [DependencyInjection] fixed #8570
return 0 if there is no valid data
merged branch dominikzogg/timecollectorfix (PR #8581)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #8581).

Discussion
----------

TimeCollector, Notice, if no events

https://github.com/symfony/symfony/issues/8574

Commits
-------

e9da1c0 return 0 if there is no valid data