RFC: refactor binder and planner

[skyzh]

Let's borrow some code from https://github.com/cmu-db/bustub

• For binder, we have too many local states, which are hard to track. e.g., for a BindXXX function, we should return a BoundXXX, instead of recording something inside the binder and use it later. This is prune to error.
• For planner, we should have a separate expression enum type. binder: separate InputRef to another expression type #693
• We should have schema for each plan node from day one. Wrong schema is causing too many problems for us. The next refactoring should also enforce schema on all plan nodes.