Added new Forwarded header support for Request::getClientIps

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11073
| License       | MIT
| Doc PR        | no
Also worth adding a test for `Forwarded: For="127.0.0.1:80"` which should return `127.0.0.1:80` (I think it does, but just for completeness' sake)