…e parser

Support slices in type reflection

Tracking issue: rust-lang#146922

This PR adds support for inspecting slices `[T]` through type reflection. It does so by adding the new `Slice` struct + variant, which is very similar to `Array` but without the `len` field:

```rust
pub struct Slice {
    pub element_ty: TypeId,
}
```

Here is an example reflecting a slice:

```rust
match const { Type::of::<[u8]>() }.kind {
    TypeKind::Slice(slice) => assert_eq!(slice.element_ty, TypeId::of::<u8>()),
    _ => unreachable!(),
}
```

In addition to this, I also re-arranged the type info unit tests.

r? @oli-obk

…nnethercote

Bump bootstrap compiler to 1.94

https://forge.rust-lang.org/release/process.html#default-branch-bootstrap-update-tuesday

…hanBrouwer

Port `#![crate_type]` to the attribute parser

Tracking issue: rust-lang#131229

~~Note that the actual parsing that is used in the compiler session is unchanged, as it must happen very early on; this just ports the validation logic.~~

Also added `// tidy-alphabetical-start` to `check_attr.rs` to make it a bit less conflict-prone

…=enthropy7

Improve error message for assert!() macro in functions returning bool

Detect `assert!()` macro in error messages and provide clearer diagnostics

When `assert!()` is used in a function returning a value, show a message explaining that `assert!()` doesn't return a value, instead of the generic "if may be missing an else clause" error.

Fixes rust-lang#151446