[native_assets_cli] Add paths to syntax views

[dcharkes]

Bug: #1826

This PR adds the path that was navigated through the JSON to the syntax classes. This makes syntax errors more descriptive: Unexpected value '123' for 'target_os'. Expected a String. -> Unexpected value '123' (int) for 'config.code.target_os'. Expected a String..

Because the data asset and code asset extensions don't know the internals of the base protocol extension, the extension points now expose both a json and a jsonPath. That path is then used to instantiate the syntax view of the extension, so it can give more precise error messages.

• For CodeConfig this comes naturally, it's a clean view.
• For EncodedAsset this is somewhat weird because it is half-used as value class: [native_assets_cli] EncodedAsset is not immutable but overrides hashCode #2045

(The next PR will add a full syntax validation pass, at which point we should be able to address #2039.)

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

[coveralls]

coverage: 86.693% (+0.05%) from 86.642%
when pulling b115edf on json-view-paths
into 10a25e3 on main.