Decide what symbols to hide from workspace symbols

[mhanberg]

Description

Many modules include "public private" functions that aren't intended for you to use and are injected with metaprogramming.

This functions often are prefixed and suffixed with a double underscore __struct__. These seem to clutter up the symbol table and make it harder to use.

I believe that IEx will hide those from autocomplete, so it might make sense to filter those in the symbol table.

Example