Auto merge of #38097 - Mark-Simulacrum:fn-sig-slice, r=eddyb

Refactor ty::FnSig to contain a &'tcx Slice<Ty<'tcx>>

We refactor this in order to achieve the following wins:

 - Decrease the size of `FnSig` (`Vec` + `bool`: 32, `&Slice` + `bool`: 24).
 - Potentially decrease total allocated memory due to arena-allocating `FnSig` inputs/output; since they are allocated in the type list arena, other users of type lists can reuse the same allocation for an equivalent type list.
 - Remove the last part of the type system which needs drop glue (#37965 removed the other remaining part). This makes arenas containing `FnSig` faster to drop (since we don't need to drop a Vec for each one), and makes reusing them without clearing/dropping potentially possible.

r? @eddyb

0 files changed, 0 insertions, 0 deletions