resolve: Module-related refactorings Extracted parts of https://github.com/rust-lang/rust/pull/156362 that don't require splitting `(Local,Extern)ModuleData` into separate data structures. - Some `expect_local` assertions are added - Methods that need to exist on all of `Module` and `(Local,Extern)Module` are implemented for `ModuleData` - Methods that need to exist on `ModuleKind` are moved to `ModuleKind` - Some unnecessary complicated logic using `graph_root` is simplified - `glob_importers` are filled and used only for local modules. - Some unnecessary logic is skipped for extern modules in `resolve_ident_in_module_non_globs_unadjusted` - Module construction functions are cleaned up - `module_to_string` is simplified r? @nnethercote