[FrameworkBundle] updated XML route description

This PR turns

```xml
<route name="route_1" path="/hello/{name}" class="Symfony\Component\Routing\Route" path_regex="#^/hello(?:/(?P&lt;name&gt;[a-z]+))?$#s">
```

into

```xml
<route name="route_1" class="Symfony\Component\Routing\Route">
    <path regex="#^/hello(?:/(?P&lt;name&gt;[a-z]+))?$#s">/hello/{name}</path>
```

in XML routing description.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7887
| License       | MIT
| Doc PR        | n/a