Add option hideNegatable to ArgParser.flag()

[mosuem]

Recreating dart-archive/args#287

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
args	Non-Breaking	2.6.1-wip	2.6.1-wip	2.6.1-wip	✔️

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

Coverage ✔️

File	Coverage
pkgs/args/lib/src/allow_anything_parser.dart	💚 75 %
pkgs/args/lib/src/arg_parser.dart	💚 94 %
pkgs/args/lib/src/option.dart	💚 93 %
pkgs/args/lib/src/usage.dart	💚 99 %

This check for test coverage is informational (issues shown here will not fail the PR).

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbols

License Headers ✔️

// Copyright (c) 2024, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

[sigurdm]

Thanks for moving this!

[mosuem]

Thanks for moving this!

Well I also closed the original ;)