LibWeb: Replace ARIA role static FlyStrings with an enum

This replaces the FlyStrings for ARIA roles that were constructed in
a [[gnu::constructor]] with a single enum. I came across this as the
DOM inspector was crashing due to a null FlyString for an ARIA role.

After fixing that, I was confused as to why these roles were not an
enum. Looking at the spec there's a fixed list of roles and switching
from references to static strings to an enum was pretty much an
exercise in find and replace :).

No functional changes (outside of fixing the mentioned crash).

Userland/Services/WebContent/WebDriverConnection.cpp

@@ -1253,7 +1253,9 @@ Messages::WebDriverClient::GetComputedRoleResponse WebDriverConnection::get_comp
     auto role = element->role_or_default();
 
     // 5. Return success with data role.
-    return DeprecatedString { role };
+    if (role.has_value())
+        return Web::DOM::ARIARoles::role_name(*role);
+    return ""sv;
 }
 
 // 12.5.1 Element Click, https://w3c.github.io/webdriver/#element-click