LibJS: Parse === and !== binary operators

Author: https://github.com/deoxxa
Commit: e88f2f15ee
Pull-request: https://github.com/SerenityOS/serenity/pull/1425
Reviewed-by: https://github.com/sunverwerth

Libraries/LibJS/Lexer.h

@@ -54,6 +54,7 @@ private:
     int m_current_char;
 
     static HashMap<String, TokenType> s_keywords;
+    static HashMap<String, TokenType> s_three_char_tokens;
     static HashMap<String, TokenType> s_two_char_tokens;
     static HashMap<char, TokenType> s_single_char_tokens;
 };