[infra] Use path dependencies between native_assets_cli and native_assets_builder in Flutter tools

[dcharkes]

Once pub supports path dependencies in pubspecs of git dependencies, we should change over the dependency on native_assets_builder and native_assets_cli to be git dependencies.

Blocked by:

• If a git path in a pubspec is relative interpret it relative to the pubspec pub#449

This would enable doing breaking changes to native_assets_cli and consuming these breaking changes in native_assets_builder in a single atomic atomic step. cc @jonasfj @sigurdm

In turn this means we could stop building against both published and path dependencies on the repo here. cc @mosuem

It also means we completely stop publishing native_assets_builder (it's already listed hidden currently).

cc @mkustermann before addressing dart-lang/pub#449, we can't have a path dependency on from one package to another in a mono-repo and succeed resolving. (Unless we use dependency_overrides in flutter_tools.)

Alternatives:

• Merge packge_native_assets_builder into native_assets_cli but in a private library. (Downside: pub get will pull in all the builder code when users have build.dart scripts.)
• Use dependency overrides in flutter_tools.
• Stop letting native_assets_builder depend on native_assets_cli. Duplicate code where necessary. (Downsides: duplicated code. Harder to test serialization/deserialization. The _builder will serialize BuildConfig and deserialize BuildOutput, while the _cli will deserialize BuildConfig and serialize BuildOutput)

This does not yet solve the issue of flutter_tools rolling into g3 separately from dartdev and g3 only having one copy of native_assets_builder (which force us to do any breaking changes in a multi step multi roll fashion). https://github.com/dart-lang/native/blob/main/pkgs/native_assets_builder/CONTRIBUTING.md#rolling

[dcharkes]

• Stop letting native_assets_builder depend on native_assets_cli. Duplicate code where necessary. (Downsides: duplicated code. Harder to test serialization/deserialization. The _builder will serialize BuildConfig and deserialize BuildOutput, while the _cli will deserialize BuildConfig and serialize BuildOutput)

@jonasfj suggested to do this. Add a script in tool/ to do the duplication, and a script in tool/ to verify that the files are copied on the CI.

[dcharkes]

In turn this means we could stop building against both published and path dependencies on the repo here.

We have already stopped this.

I don't believe we can use git dependencies in flutter_tools at this point, so we'll have to keep staggered publishing.