Native assets in other build systems are not built with `package:native_assets_builder` invoking `build.dart` scripts. Instead all packages have their own blaze rules. Therefore we'd like to not depend on `package:native_assets_builder` from flutter tools in g3 at all.

This PR aims to move the imports of `native_assets_builder` and `native_assets_cli` into the `isolated/` directory and into the files with a `main` function that are not used in with other build systems.

In order to be able to remove all imports in files used by other build systems, two new interfaces are added `HotRunnerNativeAssetsBuilder` and `TestCompilerNativeAssetsBuilder`. New parameters are then piped all the way through from the entry points:

* bin/fuchsia_tester.dart
* lib/executable.dart

The build_system/targets dir is already excluded in other build systems.

So, after this PR only the two above files and build_system/targets import from `isolated/native_assets/` and only `isolated/native_assets/` import `package:native_assets_cli` and `package:native_assets_builder`.

Context:

* https://github.com/flutter/flutter/issues/142041