Disallow re-aliasing of built-in types

[gerau]

Project

compiler

What happened?

After introducing the chumsky parser, built-in type definitions were moved out of the grammar itself. While this is an good thing, the compiler no longer throws an error for assignments like this:

type Ctx8 = u8;

In the previous parser, this behavior was disallowed:

   |
13 | type Ctx8 = u32;
   |      ^ Grammar error: unexpected builtin_alias

Note that when assigning a built-in type alias, it does not change the type, so it essentially does nothing. However, I would rather prevent users from typing this at all.