[hooks] User-defines and `dart install`

[dcharkes]

Publishing a package, takes a package out of its context, out of its workspace.

This means if a package has a resolution: workspace, that resolution is ignored once it is published and the pubspec.yaml must stand on itself.

This has implications for published CLI tools as well. If a CLI-tool is dart installed via hosted, git, or path dependency. Then the user-defines of the workspace are lost.

If the package must stand on itself after publishing, the user-defines must be duplicated in the package pubspec.yaml.

We will need to somehow communicate this to users.

(Implementation detail: dart install must ensure it respects these user-defines, even though it makes a helper package and defines that as the root of the resolution. Second implementation detail: dart install must run the build from the right resolution directory for user-defines, because user-defines may contain relative paths.)

Context:

• [cli] Introduce dart install (replacing dart pub global activate to use) sdk#60889
• [native_assets_cli] User defines #39