[REFACTOR] Standardize function interfaces in executor and reduce double pointers

[itislu]

• [ ] First merge #339

---

• Reducing the double pointers makes it more clear when list pointers are not getting moved forward.
• Move going to next cmd_table_node out of handle_builtin() to make the interface the same as handle_external_cmd().
• Reuse get_cmd_table_type_from_list() more often.
• Change interface of is_control_op_cmd_table() to align with its name.
• Reduce unnecessary intermediary variables.
• Delete get_cmd_table_from_list() and get_token_from_list() bc they are unnecessary and the code is even shorter without these function calls.

[LeaYeh]

I'm ok to change this, but I don't feel any different. Do we really need to do that?