Make fnm create global scoped environment variables in PowerShell (#667)

* Fix #664

* Remove unused import

src/shell/infer/windows.rs

@@ -1,7 +1,6 @@
 #![cfg(not(unix))]
 
 use crate::shell::Shell;
-use log::debug;
 use std::ffi::OsStr;
 use sysinfo::{ProcessExt, System, SystemExt};
 

src/shell/powershell.rs

@@ -36,11 +36,10 @@ impl Shell for PowerShell {
         };
         Ok(formatdoc!(
             r#"
-                function Set-FnmOnLoad {{ {autoload_hook} }}
-                function Set-LocationWithFnm {{ param($path); Set-Location $path; Set-FnmOnLoad }}
-                Set-Alias cd_with_fnm Set-LocationWithFnm -Force
-                Remove-Item alias:\cd
-                New-Alias cd Set-LocationWithFnm
+                function global:Set-FnmOnLoad {{ {autoload_hook} }}
+                function global:Set-LocationWithFnm {{ param($path); if ($path -eq $null) {{Set-Location}} else {{Set-Location $path}}; Set-FnmOnLoad }}
+                Set-Alias -Scope global cd_with_fnm Set-LocationWithFnm
+                Set-Alias -Option AllScope -Scope global cd Set-LocationWithFnm
                 Set-FnmOnLoad
             "#,
             autoload_hook = autoload_hook