[HttpFoundation] added constants for HTTP status code in Response

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

This adds constants for HTTP status code in Response. That's give the possibility to use constants instead of numbers in code.

These constants comes from FriendsOfSymfony/FOSRest but I think it is much better to keep them in Response as both the status texts and the constants should be synchronized.

ping @lsmith77