minor #46392 [ErrorHandler][HttpKernel] Add favicon to welcome and error pages (nicolas-grekas)

This PR was merged into the 6.2 branch.

Discussion
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[ErrorHandler][HttpKernel] Add favicon to welcome and error pages

| Q             | A
| ------------- | ---
| Branch?       | 6.2
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Similar to symfony/recipes#1023, saves some spammy http requests when displaying those pages.

Commits
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af57714fc8 [HttpKernel][ErrorHandler] Add favicon to welcome and error pages

Author: nicolas-grekas

Resources/welcome.html.php

@@ -4,6 +4,7 @@
     <meta charset="UTF-8" />
     <meta name="robots" content="noindex,nofollow,noarchive,nosnippet,noodp,notranslate,noimageindex" />
     <title>Welcome to Symfony!</title>
+    <link rel="icon" href="data:image/svg+xml,<svg xmlns=%22http://www.w3.org/2000/svg%22 viewBox=%220 0 128 128%22><text y=%221.2em%22 font-size=%2296%22>👋</text></svg>">
     <style>
         <?php $hue = random_int(0, 360); ?>
         <?php $darkColor = static function (float $alpha = 1) use ($hue) { return "hsla($hue, 20%, 45%, $alpha)"; }; ?>