LibJS: Implement bytecode generation for BigInts

Author: https://github.com/gunnarbeutner
Commit: 50ece3dd1b
Pull-request: https://github.com/SerenityOS/serenity/pull/7909
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibJS/AST.h

@@ -660,6 +660,7 @@ public:
 
     virtual Value execute(Interpreter&, GlobalObject&) const override;
     virtual void dump(int indent) const override;
+    virtual Optional<Bytecode::Register> generate_bytecode(Bytecode::Generator&) const override;
 
 private:
     String m_value;