resolve: Pre-compute non-reexport module children

Instead of repeating the same logic by walking HIR during metadata encoding.

The only difference is that we are no longer encoding `macro_rules` items, but we never currently need them as a part of this list.
They can be encoded separately if this need ever arises.

`module_reexports` is also un-querified, because I don't see any reasons to make it a query, only overhead.

Author: petrochenkov

tests/ui/macro_use_imports.fixed

@@ -16,7 +16,7 @@ extern crate macro_use_helper as mac;
 extern crate proc_macro_derive as mini_mac;
 
 mod a {
-    use mac::{pub_macro, function_macro, ty_macro, inner_mod_macro, pub_in_private_macro};
+    use mac::{pub_macro, inner_mod_macro, function_macro, ty_macro, pub_in_private_macro};
     use mac;
     use mini_mac::ClippyMiniMacroTest;
     use mini_mac;

tests/ui/macro_use_imports.stderr

@@ -22,7 +22,7 @@ error: `macro_use` attributes are no longer needed in the Rust 2018 edition
   --> $DIR/macro_use_imports.rs:19:5
    |
 LL |     #[macro_use]
-   |     ^^^^^^^^^^^^ help: remove the attribute and import the macro directly, try: `use mac::{pub_macro, function_macro, ty_macro, inner_mod_macro, pub_in_private_macro};`
+   |     ^^^^^^^^^^^^ help: remove the attribute and import the macro directly, try: `use mac::{pub_macro, inner_mod_macro, function_macro, ty_macro, pub_in_private_macro};`
 
 error: aborting due to 4 previous errors