LibWeb: Allow peeking more than 1 token ahead in CSS Parser

Author: https://github.com/AtkinsSJ
Commit: d6668dbc56
Pull-request: https://github.com/SerenityOS/serenity/pull/9073
Reviewed-by: https://github.com/TobyAsE
Reviewed-by: https://github.com/alimpfard

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

@@ -52,7 +52,7 @@ public:
 
     bool has_next_token();
     T const& next_token();
-    T const& peek_token();
+    T const& peek_token(int offset = 0);
     T const& current_token();
     void reconsume_current_input_token();