New type checker

[dalance]

After merging #1016, type checking based on invalid_factor causes to miss some type errors like:

struct A {
}

let a: logic = A;

Before #1016, Factor didn't contain type, so invalid_factor error was occurred.
After #1016, Factor can contain type, and type check is passed.

Therefore another type checking scheme is necessary.
I think the following way:

• Introduce type evaluation to Evaluator of Expression
• Check type equivalency around assignment, port connection, function call, and so on.

By introducing this way, invalid_factor and some scattered type checking logics can be removed, and some additional checks can be achieved like type or width mismatch at assignment.

Related: #1012 #76