add support for using const ty param as array size

for example:

```rust
struct A<const N: usize> {
  inner: [u8; N] // error
}
struct B<const N: usize> {
  inner: A<N> // this is fine
}
```
```
error[3-0015]: the expression is not supported yet in a const type context
  ┌─ foo.fe:2:15
  │
2 │   inner: [u8; N]
  │               ^ only literal expression is supported
```