Add internal type-alias type for improved error messages

[Vexu]

This doesn't work yet as I'd like to get approval for the concept before continuing but the goal is to (at least partially) solve #12401 by making error messages refer to the types the same way as the programmer does:

const Foo = u32; // note: type alias declared here
comptime {
    const b: Foo = 32;
    b and true; // error: expected type 'bool', found 'Foo'
}

The first commit is a general improvement required for this feature but also works separately.

[Vexu]

Rejected for complicating the compiler too much, and to possibly add an user accessible feature that provides the same benefit: #5132, #1595.

I'll open a new PR for the first commit.