[native_assets_cli] Cleanup JSON: old code config

[dcharkes]

Bug:

• [native_assets_cli] Remove fallback JSON encodings #2199

Cleanup of:

• [native_assets_cli] Provide guidance on name spacing extensions #2132

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
native_assets_cli	Breaking	0.16.0	0.17.0-wip	0.17.0	✔️

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) 2025, 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.

Unrelated files missing license headers

Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[auto-submit]

autosubmit label was removed for dart-lang/native/2221, because - The status or check suite health / changelog / run changelog health check has failed. Please fix the issues identified (or deflake) before re-applying this label.

[auto-submit]

autosubmit label was removed for dart-lang/native/2221, because - The status or check suite health / changelog / run changelog health check has failed. Please fix the issues identified (or deflake) before re-applying this label.

[coveralls]

coverage: 77.625%. first build
when pulling 8479bb4 on json-cleanup-config
into fdd7672 on main.