Remove 'pat lifetime from some match-lowering data structures

By storing `PatRange` in an Arc, and copying a few fields out of `Pat`, we can
greatly simplify the lifetimes involved in match lowering.

compiler/rustc_ty_utils/src/consts.rs

@@ -373,7 +373,8 @@ impl<'a, 'tcx> IsThirPolymorphic<'a, 'tcx> {
 
         match pat.kind {
             thir::PatKind::Constant { value } => value.has_non_region_param(),
-            thir::PatKind::Range(box thir::PatRange { lo, hi, .. }) => {
+            thir::PatKind::Range(ref range) => {
+                let &thir::PatRange { lo, hi, .. } = range.as_ref();
                 lo.has_non_region_param() || hi.has_non_region_param()
             }
             _ => false,