Design meeting: `#[export_visibility = ...]` attribute

[traviscross]

Summary

Let's read:

• RFC: #[export_visibility = ...] attribute rfcs#3834

This has been proposed for FCP.

cc @anforowicz @tmandry

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds to a possible topic of discussion that may be scheduled for deeper discussion during one of our design meetings.