[native assets] Add command-line argument for native assets yaml

[dcharkes]

Context:

• [native assets] dart test with pub workspaces sdk#60489

Currently, package:test checks for a native_assets.yaml next to the package_config.json when compiling the tests to a kernel file to embed the native assets yaml into the kernel file.

With pub workspaces, the package_config.json is no longer in the root package, rather in some parent directory.

The native_assets.yaml is in the .dart_tool/ directory of the root package.

I see two options:

• Add a command-line argument that takes the path to the native_assets.yaml to bin/test.dart.
• Add a command-line argument that takes the path to the package root to bin/test.dart. (This might be useful for other things possibly?)

Any opinions @natebosch @jakemac53?

[jakemac53]

Is the path always expected to be exactly .dart_tool/native_assets.yaml? If so we can just use that.... the test package always has to be invoked from the package root anyways