[native_assets_cli] Hide CodeAsset.type and DataAsset.type

[dcharkes]

Bug: #2132

This PR hides the asset types inside the respective extensions:

• In hooks:
  • Add extensions on EncodedAsset such as isCodeAsset to check if something is a certain asset.
  • Use the buildCodeAssets and buildDataAssets extensions everywhere.
• For BuildInput builders:
  • Use setupBuildInput from the ProtocolExtensions. (ProtocolExtension.buildAssetTypes has been made private and folded into setupBuildInput and setupLinkInput.)

This enables two things:

• Having more than one asset type per protocol, and prevent SDKs from adding in a certain asset type to the build input. (If SDKs only want to use a subset of asset types of a protocol extension, such should be configured via the constructor of protocol extension.)
• Migrating asset types, asset types can have more than one type this way. (This enables addressing [native_assets_cli] Provide guidance on name spacing extensions #2132)

Notable cleanups

• Some tests relied on passing around an identifier for which asset types to build, this is now addressed with enum BuildAssetType { code, data }.

[github-actions]

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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.

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no missing headers

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Unrelated files missing license headers

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

[coveralls]

coverage: 85.376% (+0.2%) from 85.225%
when pulling c08c236 on hide-asset-type
into 4a0fbd5 on main.