feat: inject the http session into use()

[Amoifr]

Closes #149

Injects the app's http session into ->use(), as sketched in the issue:

$browser
    ->use(function(SessionInterface $session) {
        $session->set('cart', ['product-1']);
    })
    ->visit('/cart')
    ->assertSee('product-1')
;

It works on both KernelBrowser and PlaywrightBrowser. Playwright routes browser requests through the kernel in the same process, so the container and session storage are shared the same way. The session is loaded from the session cookie when the browser has one, so the id is preserved and nothing the app stored is lost.

The session is saved, and its cookie written, when the callback returns. That happens inline in use(), so no extension hook is needed, and the callback gets the real Session object, so flash bags and other bags work as usual.

To seed the session before the first visit on Playwright, the cookie jar now falls back to the base url host when the page is still on about:blank.

[Amoifr]

Hi @kbond, this is the use(function (SessionInterface $session) { ... }) API you sketched in #149, and all 14 checks are green. Happy to rename things or reshuffle the tests if you'd like.

[kbond]

Thanks @Amoifr, nice work! I pushed a commit on top (and rebased on 1.x): PlaywrightBrowser runs the kernel in-process, so it can support this too. I moved the session support into Browser, which let the save happen inline in use() without the afterUse() hook. I also made the Playwright cookie jar fall back to the base url host before the first visit, and moved your tests to BrowserTests so they run on both browsers.