compiler: Wire {TyAnd,}Layout into rustc_abi

This finally unites TyAndLayout, Layout, and LayoutS into the same crate,
as one might imagine they would be placed. No functional changes.

compiler/rustc_abi/src/layout.rs

@@ -11,6 +11,10 @@ use crate::{
     Variants, WrappingRange,
 };
 
+mod ty;
+
+pub use ty::{FIRST_VARIANT, FieldIdx, Layout, TyAbiInterface, TyAndLayout, VariantIdx};
+
 // A variant is absent if it's uninhabited and only has ZST fields.
 // Present uninhabited variants only require space for their fields,
 // but *not* an encoding of the discriminant (e.g., a tag value).