Extract sys::args::Args implementation to sys_common

[CDirkx]

After #84413 and #84179 I have been looking into if code for sys::args::Args could be de-duplicated, as it was essentially the same on every platform: a wrapper type implementing !Send + !Sync + Debug + Iterator + ExactIterator + DoubleEndedIterator (although note that on windows and sgx the types are currently not !Send + !Sync).

This PR makes sys::args::Args a type alias (for vec::IntoIter/Empty/Clone<Iter<'static>> depending on the platform) and extracts the wrapper type to sys_common.

Alternatively, the wrapper type could be removed entirely and the type aliases used directly (i.e. only the first commit of this PR), since they are wrapped by std::env::ArgsOs anyway. These type aliases are not !Send + !Sync, but I don't know how much of a problem that would be since ArgsOs implements !Send + !Sync explicitly and currently sys::windows::args::Args and sys::sgx::args::Args are already Send and Sync.

[rust-highfive]

r? @joshtriplett

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[CDirkx]

One thing this is still blocked on is making sure the Debug output of std::env::Args and std::env::ArgsOs are not affected.

Edit: this has been resolved by relying on AsRef<[OsString]>, which in practice means that every sys::args::Args is now a type alias for vec::IntoIter.

[bors]

☔ The latest upstream changes (presumably #84525) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #84115) made this pull request unmergeable. Please resolve the merge conflicts.

[CDirkx]

warning: spurious network error (1 tries remaining): failed to get 200 response from https://crates.io/api/v1/crates/once_cell/1.7.2/download, got 503
error: failed to download from https://crates.io/api/v1/crates/difference/2.0.0/download

[bors]

☔ The latest upstream changes (presumably #85036) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #84967) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #87580) made this pull request unmergeable. Please resolve the merge conflicts.

[JohnCSimon]

Ping from triage:
@CDirkx can you please resolve the merge conflicts?

[joshtriplett]

Seems reasonable to me; r=me with conflicts addressed.

[JohnCSimon]

Ping again from triage:
@CDirkx can you please resolve the merge conflicts and after that, please set the tag to S-waiting-on-review thank you.

[Dylan-DPC]

Closing this as inactive