Tracking Issue for `#[export_visibility = ...]` attribute

This is a tracking issue for the RFC "#[export_visibility = ...] attribute" (3834-export-visibility.md). The feature gate for the issue is #![feature(export_visibility)].

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Implement the RFC: https://github.com/rust-lang/rust/pull/151431
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• Is stabilizing -Zdefault-visibility=... a prerequisite for stabilizing #[export_visibility = ...]?
• Figure out end-to-end testing for WASM: https://github.com/rust-lang/rust/issues/153364

Implementation history

• Initial PR: https://github.com/rust-lang/rust/pull/151431

Read RFC 3834 and the implementation PR #151431 first. The remaining work is to adjust documentation and prepare a stabilization PR using the linked rustc-dev-guide instructions, while resolving the questions about default visibility and end-to-end WASM testing.