[CssSelector] fully rewritted component

Squashed commits:
[CssSelector] removed previous implementation
[CssSelector] rewriting, step 1
[CssSelector] rewriting, step 2
[CssSelector] rewriting, step 3
[CssSelector] rewriting, step 4
[CssSelector] rewriting, step 5
[CssSelector] rewriting, step 6
[CssSelector] fixed shortcuts regex
[CssSelector] tests, step1
[CssSelector] tests, step2
[CssSelector] tests, step3
[CssSelector] tests, step4
[CssSelector] fixed problems based @stof's on feedback
[CssSelector] tests, step5
[CssSelector] tests, step6
[CssSelector] tests, step7
[CssSelector] added my name in composer.json
merged branch jfsimon/css-selector-rewriting (PR #7463)

This PR was merged into the master branch.

Discussion
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[CssSelector] fully rewritted component

The `CssSelector` component is a port of the Python https://github.com/SimonSapin/cssselect library. Previous implementation was a port of the `v0.1` tag, this implementation is a port of the `v0.7.1` tag. As Python and PHP have different philosophies, this is not a simple language-to-language translation, I needed to re-architecture the lib.

**Note about BC:** This new version introduces some changes making fail legacy tests.
New XPath should be equivalents, these changes are:
-  When having a condition on an class, legacy condition is prefixed with a test of class existence. Example: `[contains(@class, 'foo')]` is transformed to `[@class and contains(@class, 'foo')]`.
-  When having conditions on descendants, `/descendant::*` is transformed to `/descendant-or-self::*/*`.

I updated legacy tests (stored in `CssSelectorTest` class) accordingly.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | see above
| Deprecations? | no
| Tests pass?   | yes

Should fix #3615 and #4271

Commits
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c6f87d0 [CssSelector] fully rewritted component
Add the serializer service
[CssSelector] removed unneeded use statements
[CssSelector] removed obsolete file
[CssSelector] fixed BC break
merged branch loalf/add_serializer_service (PR #6815)

This PR was merged into the master branch.

Discussion
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[2.3] [FrameworkBundle] [Serializer] Loads the Serializer component as a service in the Framework Bundle

This PR is the same as
https://github.com/symfony/symfony/pull/5347

but since I am struggling to squash all the commits I better create a new one. Sorry for the inconveniences, :)

Commits
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b4e4844 Add the serializer service