Support pointers in type reflection
Tracking issue: rust-lang/rust#146922
This PR adds support for inspecting pointers `*const T` and `*mut T` through type reflection. It does so by adding the new `Pointer` struct + variant:
```rust
pub struct Pointer {
/// The type of the value being pointed to.
pub ty: TypeId,
/// Whether this pointer is mutable or not.
pub mutable: bool,
}
```
This can be gathered using `Type::of`, for example:
```rust
match const { Type::of::<*const u8>() }.kind {
TypeKind::Pointer(pointer) => {
assert_eq!(pointer.ty, TypeId::of::<u8>());
assert!(!pointer.mutable);
}
_ => unreachable!(),
}
```
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