bug #19922 [Yaml][TwigBridge] Use JSON_UNESCAPED_SLASHES for lint commands output (chalasr)

This PR was merged into the 2.7 branch.

Discussion
----------

[Yaml][TwigBridge] Use JSON_UNESCAPED_SLASHES for lint commands output

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Slashes are escaped when sing the `lint:twig` and `lint:yaml` commands with the `format` option set to `json`, giving such results:

```json
[
    {
        "file": "yaml\/wrong\/1.yml",
        "valid": false,
        "message": "Unable to parse at line 1 (near \";:cc`\")."
    }
]
```

That's not convenient as file paths may be reused (e.g. copy-pasted).
Results stay fine as error messages are already escaped:

```json
[
    {
        "file": "yaml/wrong/1.yml",
        "valid": false,
        "message": "Unable to parse at line 1 (near \";:cc`\")."
    }
]
```

Commits
-------

0427594 Use JSON_UNESCAPED_SLASHES for lint commands output

Author: fabpot

Command/YamlLintCommand.php

@@ -156,7 +156,7 @@ private function displayJson(OutputInterface $output, $filesInfo)
             }
         });
 
-        $output->writeln(json_encode($filesInfo, defined('JSON_PRETTY_PRINT') ? JSON_PRETTY_PRINT : 0));
+        $output->writeln(json_encode($filesInfo, defined('JSON_PRETTY_PRINT') ? JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES : 0));
 
         return min($errors, 1);
     }