rustdoc: Tracking issue for command-line flag `--no-capture`

A command line option to prevent rustdoc from capturing the stdout/stderr output from doctests.

[!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

• Implementation PR
• Stabilization PR

Unresolved questions

• Should we reject --no-capture if --test wasn't passed? Note that we don't so for similar flags (e.g., --test-args), so it's probably moot. We could/should however at least warn in such cases.
• If we rename --nocapture to --no-capture (#148115), should we keep around the old version for a while in a soft-deprecated then hard-deprecated state?
• I think the original intention was to update Cargo to use this flag instead of --test-args --no-capture / --test-args --nocapture. However the relevant PR was closed (https://github.com/rust-lang/cargo/pull/9705). How should we proceed?

Implementation history

• https://github.com/rust-lang/rust/pull/86230
• https://github.com/rust-lang/rust/pull/148115

Start by reviewing implementation PRs #86230 and #148115, then inspect the rustdoc command-line handling and the related Cargo context from PR #9705. Resolve the listed stabilization questions and prepare the stabilization PR; done means the flag's behavior and any compatibility or warning policy are settled.