add a new command to query the registry on windows (#6670)

* add a new command to query the registry on windows

* cross platform tweaks

* return nushell datatype

* change visibility of exec and registry commands

crates/nu-command/src/default_context.rs

@@ -158,12 +158,17 @@ pub fn create_default_context() -> EngineState {
         bind_command! {
             Benchmark,
             Complete,
-            Exec,
             External,
             NuCheck,
             Sys,
         };
 
+        #[cfg(unix)]
+        bind_command! { Exec }
+
+        #[cfg(windows)]
+        bind_command! { RegistryQuery }
+
         #[cfg(any(
             target_os = "android",
             target_os = "linux",