Perform indexing during lowering.

Do not access DefId<->HirId maps before they are initialized.

compiler/rustc_middle/src/arena.rs

@@ -92,9 +92,6 @@ macro_rules! arena_types {
             [] tys: rustc_middle::ty::TyS<$tcx>,
             [] predicates: rustc_middle::ty::PredicateInner<$tcx>,
 
-            // HIR query types
-            [] indexed_hir: rustc_middle::hir::IndexedHir<$tcx>,
-
             // Note that this deliberately duplicates items in the `rustc_hir::arena`,
             // since we need to allocate this type on both the `rustc_hir` arena
             // (during lowering) and the `librustc_middle` arena (for decoding MIR)