Use the correct cssselect library name in docblocks.

The original python library is called cssselect, not cssselector.
Update the note about origins of the CssSelector component.

The last rewrite is based on the cssselect which is no longer part of lxml, but was extracted as an independent library.
minor #13132 [CssSelector] Use the correct cssselect library name in docblocks. (jakzal)

This PR was merged into the 2.3 branch.

Discussion
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[CssSelector] Use the correct cssselect library name in docblocks.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | #11894
| License       | MIT
| Doc PR        | -

As suggested in #11894, the original python library is called [cssselect](https://github.com/SimonSapin/cssselect), not cssselector.

I also updated the README, as the cssselect was extracted as an independent library and it's no longer part of lxml.

Commits
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55f0d9e Update the note about origins of the CssSelector component.
1997b12 Use the correct cssselect library name in docblocks.
[HttpFoundation] fixed error when an IP in the X-Forwarded-For HTTP header contains a port
[Debug] fix checkip6
bug #12572 [HttpFoundation] fix checkip6 (Neime)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #12572).

Discussion
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[HttpFoundation] fix checkip6

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

I have this error ContextErrorException: Warning: inet_pton(): Unrecognized address X.X.X.X:X
in IpUtils.php line 110

X.X.X.X:X is detected as a ipv6 because HTTP_X_FORWARDED_FOR have a port.

Commits
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1da0ba4 [Debug] fix checkip6
bug #13114 [HttpFoundation] fixed error when an IP in the X-Forwarded-For HTTP head... (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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[HttpFoundation] fixed error when an IP in the X-Forwarded-For HTTP head...

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

On symfony.com, we have errors related to IP addresses in the `X-Forwarded-For` HTTP header that have a port. If that happens (I have no ideas what is doing that), the page crashes with an error like `inet_pton(): Unrecognized address 187.65.229.211:63479` (which comes from IpUtils::checkIpv6()). This fixes the root cause by removing the port.

#12572 is solving the consequence and I propose to also merge it.

Commits
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60ad382 [HttpFoundation] fixed error when an IP in the X-Forwarded-For HTTP header contains a port
[TwigBundle] Moved the setting of the default escaping strategy from the Twig engine to the Twig environment
bug #13141 [TwigBundle] Moved the setting of the default escaping strategy from the Twig engine to the Twig environment (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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[TwigBundle] Moved the setting of the default escaping strategy from the Twig engine to the Twig environment

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11773
| License       | MIT
| Doc PR        | n/a

The default escaping strategy was set on the Twig Engine and not the Twig Environment. That's a problem under some circumstances (like what #11773 describes), but it's also much better to set everything on the Twig  Environment directly.

Commits
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91b24e8 [TwigBundle] Moved the setting of the default escaping strategy from the Twig engine to the Twig environment
Fixes various phpdoc and coding standards.