Tracking Issue for Rustdoc support of RFC3485 `feature-documentation`

This is a tracking issue for Rustdoc support of the RFC "feature-documentation" (rust-lang/rfcs#3485).

[!NOTE]

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.
Instead, open a dedicated issue for the specific matter or post in the #t-rustdoc Zulip channel.

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

• Provide a way for rustdoc to consume this new information
• Display a new feature table in some way
• Add support to rustdoc JSON output
• Adjust documentation (see instructions on rustc-dev-guide)
• Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

• Everything!

Implementation history

Start by reading RFC 3485 and the rustdoc-related checklist in this issue. The work spans consuming the new information, displaying a feature table, rustdoc JSON output, documentation, style guidance, and stabilization. Because the unresolved questions say “Everything!” and no files or tests are identified, a newcomer should first determine the design and implementation scope before coding.