Improve the workspace awareness by using child crate's "workspace" Cargo.toml key if present

[andrewdavidmackenzie]

I understand that a child crate in a workspace can include a "workspace" key with a path - that points directly to the workspace root folder (where the workspace's Cargo.toml file should reside).

This means the parent folder doesn't have to be a direct parent of the current crate, and could be in a "sibling" (or child, which would be weird) folder on the file system.