* fix: absolutize path against its parent if it was a symlink.
On Linux this happens because Rust calls readlink but doesn't canonicalize the resultant path.
* feat: playground function to create symlinks
* fix: use playground dirs
* feat: test for #1631, shift tests names
* Custom canonicalize method for FilesystemShell.
* Use custom canonicalize method.
Fixed missing import.
* Move function body to already impl body.
* Create test that aims to resolve.
This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).
