Preloads with a top-level namespace don't load macros

[lilactown]

See https://github.com/lilactown/bug-shadow-macro-repl for a reproduction.

I noticed https://github.com/thheller/shadow-cljs/issues/1059 which seems to be directly related. I changed the code to use more than a single part (e.g. bug-shadow.macro-repl) and it resolved the bug.

In a project I work on, we have a top-level namespace that we use frequently from the REPL. It would be helpful to have a macro available from within it, but currently this blocks us from easily doing so.