Replace ichwh with which and some fixes for auto-cd (canonicalization) (#1672)

* 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

* Creation of FilesystemShell with custom location may fail

* Replace ichwh with which

* Creation of FilesystemShell with custom location may fail

* Replace ichwh with which

* fix: add ichwh again since it cannot be completely replaced

* fix: replace one more use of which

crates/nu-cli/src/commands/classified/external.rs

@@ -467,12 +467,12 @@ fn spawn(
 async fn did_find_command(name: &str) -> bool {
     #[cfg(not(windows))]
     {
-        ichwh::which(name).await.unwrap_or(None).is_some()
+        which::which(name).is_ok()
     }
 
     #[cfg(windows)]
     {
-        if ichwh::which(name).await.unwrap_or(None).is_some() {
+        if which::which(name).is_ok() {
             true
         } else {
             let cmd_builtins = [

crates/nu-cli/src/commands/classified/internal.rs

@@ -117,7 +117,7 @@ pub(crate) fn run_internal_command(
                     }
                     CommandAction::EnterShell(location) => {
                         context.shell_manager.insert_at_current(Box::new(
-                            FilesystemShell::with_location(location, context.registry().clone()),
+                            FilesystemShell::with_location(location, context.registry().clone())?,
                         ));
                     }
                     CommandAction::AddAlias(name, args, block) => {

crates/nu-cli/src/commands/run_external.rs

@@ -181,7 +181,7 @@ async fn maybe_autocd_dir<'a>(cmd: &ExternalCommand, ctx: &mut Context) -> Optio
         || (cmd.args.is_empty()
             && PathBuf::from(name).is_dir()
             && dunce::canonicalize(name).is_ok()
-            && ichwh::which(&name).await.unwrap_or(None).is_none())
+            && which::which(&name).is_err())
     {
         Some(name)
     } else {