Hide alias (#4432)

* Add alias interning

Now, AliasId is used to reference aliases stored in EngineState, similar
to decls, blocks, etc.

* Fix wrong message

* Fix using decl instead of alias

* Extend also alias id visibility

* Merge also aliases from delta

* Add alias hiding code

Does not work yet but passes tests at least.

* Fix wrong alias lookup and visibility appending

* Add hide alias tests

* Fmt & Clippy

* Fix random clippy warnings in "which" command

crates/nu-command/src/system/which_.rs

@@ -82,9 +82,9 @@ fn get_entries_in_aliases(engine_state: &EngineState, name: &str, span: Span) ->
         .into_iter()
         .map(|spans| {
             spans
-                .into_iter()
+                .iter()
                 .map(|span| {
-                    String::from_utf8_lossy(engine_state.get_span_contents(&span)).to_string()
+                    String::from_utf8_lossy(engine_state.get_span_contents(span)).to_string()
                 })
                 .join(" ")
         })