Implement read_buf for TcpStream, Stdin, StdinLock, ChildStdout,
ChildStderr (and internally for AnonPipe, Handle, Socket), so
that it skips buffer initialization.

The other provided methods like read_to_string and read_to_end are
implemented in terms of read_buf and so benefit from the optimization
as well.

This commit also implements read_vectored and is_read_vectored where
applicable.

This reverts commit e63ec2e.

…-Simulacrum

Inline `Poll` methods

With `opt-level="z"`, the `Poll::map*` methods are sometimes not inlined (see <https://godbolt.org/z/ca5ajKTEK>). This PR adds `#[inline]` to these methods. I have a project that can benefit from this change, but do we want to enable this behavior universally?

Fixes rust-lang#101080.

Implement read_buf for a few more types

Implement read_buf for TcpStream, Stdin, StdinLock, ChildStdout,
ChildStderr (and internally for AnonPipe, Handle, Socket), so
that it skips buffer initialization.

The other provided methods like read_to_string and read_to_end are
implemented in terms of read_buf and so benefit from the optimization
as well.

This commit also implements read_vectored and is_read_vectored where
applicable.

… r=pietroalbini

Re-apply "switch to the macos-12-xl builder"

This reverts commit e63ec2e, essentially re-applying fcbae98.

r? `@pietroalbini`

…r=compiler-errors

Make `match` arm comma suggestion more clear

Fixes rust-lang#108472

Merge diagnostic_items duplicate diagnostics

To deduplicate how we diagnose duplication.

…ddle

Clean up JS files code a bit

I mostly moved values closer to where they are used to make the code reading easier.

r? ``@notriddle``