Explain unusual debugging code in librustc

Introduced in #47828 to help track down some bugs, it landed a bit hastily so
this is intended on cleaning it up a bit.

Author: alexcrichton

src/librustc_resolve/resolve_imports.rs

@@ -1026,9 +1026,14 @@ fn import_path_to_string(names: &[SpannedIdent],
         if names.is_empty() {
             import_directive_subclass_to_string(subclass)
         } else {
-            let x = format!("{}::{}",
-                     names_to_string(names),
-                     import_directive_subclass_to_string(subclass));
+            // Note that this code looks a little wonky, it's currently here to
+            // hopefully help debug #48116, but otherwise isn't intended to
+            // cause any problems.
+            let x = format!(
+                "{}::{}",
+                names_to_string(names),
+                import_directive_subclass_to_string(subclass),
+            );
             assert!(!names.is_empty());
             assert!(!x.starts_with("::"));
             return x