std: reorganize pipe implementations

[joboet]

Currently, there are two distinct types called AnonPipe in std:

• The one used to implement io::pipe (in sys::anonymous_pipe)
• The one used to implement Stdin/Stdout/Stderr (in sys::pal::pipe)

On Windows, these actually have different semantics, as one of the handles returned by the sys::pal::pipe version is opened for asynchronous operation in order to support read2, whereas the sys::anonymous_pipe version does not do so. Thus the naming is extremely confusing.

To fix this, this PR renames the sys::anonymous_pipe version of AnonPipe to simply Pipe, whereas the sys::pal::pipe version is now called ChildPipe. Additionally,

• sys::anonymous_pipe is now also just called sys::pipe.
• On Windows, sys::pal::pipe has been moved to sys::process and is now called sys::process::child_pipe.
• On non-Windows platforms, pipe creation is now exclusively handled by sys::pipe and ChildPipe is defined as a type alias to Pipe within sys::process.

And lastly, the read2 function (originally in sys::pal::pipe) is now called read_output and defined by sys::process, as (at least on Windows) it is only usable with ChildPipe.

Includes #146639 for convenience.

[rustbot]

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[thaliaarchi]

I opened these two PRs before I noticed your PR here, which is a superset, modulo some tiny fixes for tier 3 builds in mine. Sorry. My PRs probably create more work for you, so feel free to close them. But if they'd help to split yours for review, they might be useful.

• Fix unsupported std::sys::thread after move #146800
• Move pipe into sys #146801

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[RalfJung]

Sorry for those test failures, I'll adjust this a bit on the Miri side to hopefully make it more resilient without being terribly slow.

[bors]

☔ The latest upstream changes (presumably #146931) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #147782) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #149039) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.