Rollup merge of #113534 - oli-obk:simd_shuffle_dehackify, r=workingjubilee

Forbid old-style `simd_shuffleN` intrinsics

Don't merge before https://github.com/rust-lang/packed_simd/pull/350 has made its way to crates.io

We used to support specifying the lane length of simd_shuffle ops by attaching the lane length to the name of the intrinsic (like `simd_shuffle16`). After this PR, you cannot do that anymore, and need to instead either rely on inference of the `idx` argument type or specify it as `simd_shuffle::<_, [u32; 16], _>`.

r? `@workingjubilee`

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -305,7 +305,7 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                             terminator.kind = TerminatorKind::Unreachable;
                         }
                     }
-                    _ if intrinsic_name.as_str().starts_with("simd_shuffle") => {
+                    sym::simd_shuffle => {
                         validate_simd_shuffle(tcx, args, terminator.source_info.span);
                     }
                     _ => {}