[native_assets_builder] Support pub workspaces 2

[dcharkes]

Closes: #1905

This does a bigger refactoring to take runPackageName into account when checking for "if there are packages with native assets".

It changes the public API in the following way:

• PackageLayout no longer has methods for if packages have hooks, as it does not take into account the dependency graph
• NativeAssetsBuildRunner now exposes a method to query whether any packages in the dependencies have build hooks
• (The implementation is in the BuildPlanner, and this class stays internal.)

This means that PackageLayout has the API to provide the right package layout to the NativeAssetsBuildRunner, and the NativeAssetsBuildRunner has the methods to be queried by embedders/launchers.

[github-actions]

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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
// BSD-style license that can be found in the LICENSE file.

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

[coveralls]

coverage: 83.877% (+0.04%) from 83.842%
when pulling 549efc9 on nab-pub-workspaces-take-2
into 3849808 on main.

[coveralls]

coverage: 83.877% (+0.04%) from 83.842%
when pulling 4459491 on nab-pub-workspaces-take-2
into 3849808 on main.

[mosuem]

Nested awaits do make my skin crawl a bit ;)

[mosuem]

Perhaps

final planner = await _planner;
final packagesWithHook = await planner.packagesWithHook(Hook.build);

further above could be extracted to a method to alleviate this here and in other places, as the _planner is mostly accessed to run packagesWithHook. Just a nit.

[dcharkes]

Agreed with the skin crawl, I already adopted final planner = await _planner; in other places.

[dcharkes]

Thanks @mosuem!