* 3.2:
fixed tests
fixed merge
Fix minor phpdoc mismatches with the code(detected by phan)
[Asset] Starting slash should indicate no basePath wanted
[Security] Fix phpdoc logout listener
[EventDispatcher] fix getting priorities of listeners during dispatch
Add iconv extension to suggested dependencies
Fix minor typo in the main README.md
Allow Upper Case property names in ObjectNormalizer
[EventDispatcher] fix: unwrap listeners for correct info
This PR was squashed before being merged into the 3.3-dev branch (closes#21478).
Discussion
----------
[Asset] Add support for preloading with links and HTTP/2 push
| Q | A
| ------------- | ---
| Branch? | master
| Bug fix? | no
| New feature? | yes
| BC breaks? | no
| Deprecations? | no
| Tests pass? | yes
| Fixed tickets | n/a
| License | MIT
| Doc PR | todo
Allows compatible clients to preload mandatory assets like scripts, stylesheets or images according to [the "preload" working draft of the W3C](https://www.w3.org/TR/preload/).
Thanks to this PR, Symfony will automatically adds `Link` HTTP headers with a `preload` relation for mandatory assets. If an intermediate proxy supports HTTP/2 push, it will convert preload headers. For instance [Cloudflare supports this feature](https://blog.cloudflare.com/using-http-2-server-push-with-php/).
It dramatically increases pages speed and make the web greener because only one TCP connection is used to fetch all mandatory assets (decrease servers and devices loads, improve battery lives).
Usage:
Updated version:
```html
<html>
<body>
Hello
<script src="{{ preload(asset('/scripts/foo.js'), 'script') }}"></script>
</body>
</html>
```
~~First proposal:~~
```html
<html>
<body>
Hello
<script src="{{ preloaded_asset('/scripts/foo.js', 'script') }}"></script>
</body>
</html>
```
- [x] Add tests
Commits
-------
7bab21700d [Asset] Add support for preloading with links and HTTP/2 push
