- Closes#1557.
- Replaces `executableURL` utility function for getting app executable
path with `executablePath`.
- Adds `FilePath.resolvingSymlinks()` extension.
- Also converts for FilePath for types in `ContainerVersion` target.
- Sets up API server as source of truth for installation root, similarly
to what was done for the data root. `system start` establishes the
install root, setting the environment variable `CONTAINER_INSTALL_ROOT`
when launching the API server.
- The API server propagates the environment variable when launching
helpers, and returns the install root to the CLI via the health check
XPC.
- Includes several fixes for detecting plugins that use app bundle
layout.