Move some Map methods onto TyCtxt.

The end goal is to eliminate `Map` altogether.

I added a `hir_` prefix to all of them, that seemed simplest. The
exceptions are `module_items` which became `hir_module_free_items` because
there was already a `hir_module_items`, and `items` which became
`hir_free_items` for consistency with `hir_module_free_items`.

compiler/rustc_monomorphize/src/collector.rs

@@ -478,7 +478,7 @@ fn collect_items_rec<'tcx>(
             );
             recursion_depth_reset = None;
 
-            let item = tcx.hir().item(item_id);
+            let item = tcx.hir_item(item_id);
             if let hir::ItemKind::GlobalAsm(asm) = item.kind {
                 for (op, op_sp) in asm.operands {
                     match op {