[HttpFoundation][FrameworkBundle] Add CIDR notation support in trusted proxy list

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7312, #7262
| License       | MIT
| Doc PR        | symfony/symfony-docs#2287

Should be rebased once #7734 is merged.