Auto merge of #24920 - alexcrichton:duration, r=aturon

This commit is an implementation of [RFC 1040][rfc] which is a redesign of the
currently-unstable `Duration` type. The API of the type has been scaled back to
be more conservative and it also no longer supports negative durations.

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/1040-duration-reform.md

The inner `duration` module of the `time` module has now been hidden (as
`Duration` is reexported) and the feature name for this type has changed from
`std_misc` to `duration`. All APIs accepting durations have also been audited to
take a more flavorful feature name instead of `std_misc`.

Closes #24874

diff --cc src/libstd/sys/windows/mod.rs
Simple merge

diff --cc src/libstd/thread/mod.rs
Simple merge

diff --cc src/libtest/lib.rs
Simple merge

diff --cc src/test/bench/msgsend-ring-mutex-arcs.rs
Simple merge