LibWeb+LibWebView+WebContent: Add APIs to manage an autoplay allowlist

The spec defines a Permissions Policy to control some browser behaviors
on a per-origin basis. Management of these permissions live in their own
spec: https://w3c.github.io/webappsec-permissions-policy/

This implements a somewhat ad-hoc Permissions Policy for autoplaying
media elements. We will need to implement the entire policy spec for
this to be more general.

Userland/Libraries/LibWebView/OutOfProcessWebView.h

@@ -43,6 +43,8 @@ public:
     OrderedHashMap<DeprecatedString, DeprecatedString> get_session_storage_entries();
 
     void set_content_filters(Vector<DeprecatedString>);
+    void set_autoplay_allowed_on_all_websites();
+    void set_autoplay_allowlist(Vector<String>);
     void set_proxy_mappings(Vector<DeprecatedString> proxies, HashMap<DeprecatedString, size_t> mappings);
     void connect_to_webdriver(DeprecatedString const& webdriver_ipc_path);