Add docs for the test crate with the std docs

[ollie27]

If the compiler docs aren't going to include the test crate then it may as well be included with std.

Fixes #49388

[Mark-Simulacrum]

cc @rust-lang/docs, if you want this change I believe it's correct in terms of code.

[QuietMisdreavus]

We've already been shipping docs for test and proc_macro with the std docs, right? Does this even affect proc_macro at all?

[ollie27]

The current list of crates we ship docs for is alloc, core, proc_macro, std and std_unicode as can be seen on https://doc.rust-lang.org/1.25.0/std/. This is just adding test to that list.

[ollie27]

This will need backporting to beta now if this is accepted.

[pietroalbini]

@rust-lang/docs, can we get a decision on this PR? Thanks!

[steveklabnik]

@rfcbot: merge

I'd like to move that we accept this. People are confused about where to find these docs on IRC fairly often.

[QuietMisdreavus]

Manual tickyboxes activate!

@steveklabnik wants to merge this PR. See the post above for explanation.

• @steveklabnik
• @QuietMisdreavus
• @frewsxcv
• @GuillaumeGomez

[frewsxcv]

unanimous docs team approval! ✅

@bors r=steveklabnik,QuietMisdreavus,frewsxcv,GuillaumeGomez

[bors]

📌 Commit e719bb0 has been approved by steveklabnik,QuietMisdreavus,frewsxcv,GuillaumeGomez

[frewsxcv]

@bors rollup