refactor: Use clap to suggest alternative argument for unsupported arguments

[weihanglo]

What does this PR try to resolve?

Part of #11702.

This pull request replaces manual errors with clap native UnknownArgumentValueParser::suggest to give uses alternative arugments, including

• Suggest --no-fail-fast for --keep-going in cargo test and cargo bench.
• Suggest cargo-vendor vendor for unsupported cargo tree arguments
  • --no-merge-sources
  • --relative-path
  • --only-git-deps
  • --disallow-duplicates

This PR also renames fn arg_jobs(…) and friends to more reasonable names.

How should we test and review this PR?

cargo t --keep-going
cargo vendor --no-merge-sources
cargo vendor --relative-path
cargo vendor --only-git-deps
cargo vendor --disallow-duplicates

Before

$ cargo vendor --no-merge-sources
error: the crates.io `cargo vendor` command has now been merged into Cargo itself
and does not support the flag `--no-merge-sources` currently; to continue using the flag you
can execute `cargo-vendor vendor ...`, and if you would like to see this flag
supported in Cargo itself please feel free to file an issue at
https://github.com/rust-lang/cargo/issues/new

After

$ cargo vendor --no-merge-sources
error: unexpected argument '--no-merge-sources' found

  tip: the crates.io `cargo vendor` command has been merged into Cargo
  tip: and the flag `--no-merge-sources` isn't supported currently
  tip: to continue using the flag, execute `cargo-vendor vendor ...`
  tip: to suggest this flag supported in Cargo, file an issue at <https://github.com/rust-lang/cargo/issues/new>

Usage: cargo vendor [OPTIONS] [path]

For more information, try '--help'.

[rustbot]

r? @epage

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[weihanglo]

This is current blocked on clap-rs/clap#5081.

[epage]

This is current blocked on clap-rs/clap#5081.

This can be worked around on the clap side. We could add to the prelude a maybe_flag function that calls try_get_one and filters out the type-discrepancy error.

[weihanglo]

@epage this is ready for review. Moved some functional tests to UI tests since it makes more sense matching the entire clap output there.

[weihanglo]

Blocked on #12539 bumping the version of cargo.

[epage]

@bors r+

[bors]

📌 Commit a31aaac has been approved by epage

It is now in the queue for this repository.

[bors]

⌛ Testing commit a31aaac with merge a4c5f11...

[bors]

💔 Test failed - checks-actions

[epage]

@bors r+

[bors]

📌 Commit 77da514 has been approved by epage

It is now in the queue for this repository.

[bors]

⌛ Testing commit 77da514 with merge 50ba4bf...

[bors]

☀️ Test successful - checks-actions
Approved by: epage
Pushing 50ba4bf to master...

[bors]

☀️ Test successful - checks-actions
Approved by: epage
Pushing 50ba4bf to master...

[bors]

👀 Test was successful, but fast-forwarding failed: 422 Changes must be made through a pull request.