…k() (dunglas)

This PR was squashed before being merged into the 4.2-dev branch (closes #28875).

Discussion
----------

[FWBundle] Add a new method AbstractController::addLink()

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      |no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | n/a   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | todo

This provides a convenient method to add `Link` headers to the current `Response` directly from the `Request` object.
It improves the developer experience and the discoverability of [the WebLink component](symfony/symfony-docs#10309).

Usage:

```php
namespace App\Controller;

use Fig\Link\Link;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class MyAction extends AbstractController
{
    public function __invoke(Request $request): Response
    {
        $this->addLink($request, new Link('mercure', 'https://demo.mercure.rocks'));

        return $this->json(['foo' => 'bar']);
    }
}
```

Commits
-------

4d20c39f70 [FWBundle] Add a new method AbstractController::addLink()

…k() (dunglas)

This PR was squashed before being merged into the 4.2-dev branch (closes #28875).

Discussion
----------

[FWBundle] Add a new method AbstractController::addLink()

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      |no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | n/a   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | todo

This provides a convenient method to add `Link` headers to the current `Response` directly from the `Request` object.
It improves the developer experience and the discoverability of [the WebLink component](symfony/symfony-docs#10309).

Usage:

```php
namespace App\Controller;

use Fig\Link\Link;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class MyAction extends AbstractController
{
    public function __invoke(Request $request): Response
    {
        $this->addLink($request, new Link('mercure', 'https://demo.mercure.rocks'));

        return $this->json(['foo' => 'bar']);
    }
}
```

Commits
-------

4d20c39 [FWBundle] Add a new method AbstractController::addLink()

This PR was merged into the 3.4 branch.

Discussion
----------

Add docs for the WebLink component

The WebLink component is available since Symfony 3.3, but I never took the time to add the docs (however, a blog post explaining how to use it was available).

This documentation is based on https://dunglas.fr/2017/10/symfony-4-http2-push-and-preloading/.
If necessary, I can grant any copyright regarding this post to the Symfony project.

symfony/symfony#21478
symfony/symfony#22273
Closes #7515.

Commits
-------

91ee3bc Fix RST
ea7b3da @nicolas-grekas' review
38fda88 fix build
e12e776 RST
088690f Fix link
e3d4036 RST
178821e refactor
9f4ae9b fix typo
6beb4eb Add docs for the WebLink component