LibJS: Implement abstract equality and inequality

Author: https://github.com/0xtechnobabble
Commit: https://github.com/SerenityOS/serenity/commit/dfbaa8e5432
Pull-request: https://github.com/SerenityOS/serenity/pull/1470
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/oriko1010

Libraries/LibJS/AST.h

@@ -248,6 +248,8 @@ enum class BinaryOp {
     Slash,
     TypedEquals,
     TypedInequals,
+    AbstractEquals,
+    AbstractInequals,
     GreaterThan,
     GreaterThanEquals,
     LessThan,