…r1337)

This PR was squashed before being merged into the 6.3 branch.

Discussion
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[HttpFoundation] Add IpUtils::isPrivateIp

| Q             | A
| ------------- | ---
| Branch?       | 6.3
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | N/A
| License       | MIT
| Doc PR        | symfony/symfony-docs#18102

This is only my second PR for this project, so I hope I followed all the guidelines correctly.
Recently I had more and more use cases where I had to make exceptions (mostly rate limiting) for private IP ranges.

Symfony currently does not provide an easy way to check if an IP is private or public but implements such logic internally (private constant) for the [NoPrivateNetworkHttpClient](https://github.com/symfony/symfony/blob/6.3/src/Symfony/Component/HttpClient/NoPrivateNetworkHttpClient.php).

This PR intents to make the private subnet list reusable by adding it to [IpUtils](https://github.com/symfony/symfony/blob/6.3/src/Symfony/Component/HttpFoundation/IpUtils.php).

In the original PR of the NoPrivateNetworkHttpClient it was also briefly mentioned that this constant may have value when made public. #35566 (comment)

I think symfony should and always should have exposed this constant.

Commits
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6471582 [HttpFoundation] Add IpUtils::isPrivateIp