[CssSelectorBridge] Retrieve metadata for social media embeds (#3602, #3687) (#3706)

* [CssSelectorBridge] Metadata from social embed (#3602, #3687)

Implement the following metadata sources:
 - Facebook Open Graph
 - Twitter <meta> tags
 - Standard <meta> tags
 - JSON linked data (ld+json)

The following metadata is supported:
 - Canonical URL (may help removing garbage from URLs)
 - Article title
 - Truncated summary
 - Published/Updated timestamp
 - Enclosure/Thumbnail image
 - Author Name or Twitter handle

SitemapBridge will also automatically benefit from this commit.

* [php8backports] Add array_is_list()

Needed this function for ld+json implementation in CssSelectorBridge.

* [SitemapBridge] Add option to discard thumbnail

* [CssSelectorBridge] Fix linting issues

lib/php8backports.php

@@ -54,3 +54,13 @@ if (!function_exists('str_contains')) {
         return $needle !== '' && mb_strpos($haystack, $needle) !== false;
     }
 }
+
+if (!function_exists('array_is_list')) {
+    function array_is_list(array $arr)
+    {
+        if ($arr === []) {
+            return true;
+        }
+        return array_keys($arr) === range(0, count($arr) - 1);
+    }
+}