Support arrays in type reflection
Tracking issue: rust-lang/rust#146922
This PR adds support for inspecting arrays `[T; N]` through type reflection. It does so by adding `TypeKind::Array` and the `Array` struct:
```rust
pub struct Array {
pub element_ty: TypeId,
pub len: usize,
}
```
This can be used to inspect arrays like so:
```rust
match const { Type::of::<[u16; 4]>() }.kind {
TypeKind::Array(array) => {
assert_eq!(array.element_ty, TypeId::of::<u16>());
assert_eq!(array.len, 4);
}
_ => unreachable!(),
}
```
r? @oli-obk
a8e3ce50b9