Warn on duplicate defalias'

I would like to work on this issue if that is ok?

Sure!

You can basically copy the approach of var warnings: https://github.com/clojure/core.typed/blob/master/module-check/src/main/clojure/clojure/core/typed/var_env.clj#L58-L64

This is the equivalent file for aliases: https://github.com/clojure/core.typed/blob/master/module-check/src/main/clojure/clojure/core/typed/name_env.clj

Also add a test here: https://github.com/clojure/core.typed/blob/master/module-check/src/test/clojure/clojure/core/typed/test/core.clj

Added a patch

No longer possible single defalias is collected at runtime.