Support --workspace flag as an alias for --all

[bstrie]

cargo fmt supports a --all flag for operating on all members in a workspace. cargo check also supports --all for the same purpose, but this is deprecated in favor of --workspace, which is an alias with no semantic difference. Other tools based on cargo check, like cargo clippy, inherit the ability to use --workspace. The inability to use --workspace in an official tool thus feels inconsistent.

For reference, here's the PR where cargo clippy switched to using cargo check's manifest handling, which had the effect of removing their own bespoke --all flag: rust-lang/rust-clippy#2585 .

It would be nice for all of the officially-provided tools to present consistent interfaces.

[ytmimi]

Thanks for reaching out, but this is a duplicate of #5010