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`.

src/librustdoc/passes/calculate_doc_coverage.rs

@@ -232,7 +232,7 @@ impl DocVisitor<'_> for CoverageCalculator<'_, '_> {
                     .item_id
                     .as_def_id()
                     .and_then(|def_id| self.ctx.tcx.opt_parent(def_id))
-                    .and_then(|def_id| self.ctx.tcx.hir().get_if_local(def_id))
+                    .and_then(|def_id| self.ctx.tcx.hir_get_if_local(def_id))
                     .map(|node| {
                         matches!(
                             node,