LibWeb: Return FlyString from CSS::Parser::Token::ident

Instead of a StringView. This allows us to preserve the nice O(1) string
compare property of FlyString, and not needing to allocate when one is
needed.

Ideally all other places in Token should have similar changes done, but
to prevent a huge amount of churn, just change ident for now.

Userland/Libraries/LibWeb/CSS/Parser/Token.h

@@ -59,10 +59,10 @@ public:
     Type type() const { return m_type; }
     bool is(Type type) const { return m_type == type; }
 
-    StringView ident() const
+    FlyString const& ident() const
     {
         VERIFY(m_type == Type::Ident);
-        return m_value.bytes_as_string_view();
+        return m_value;
     }
 
     StringView function() const