Allow modules to use other modules (#6162)

* Allow private imports inside modules

Can call `use ...` inside modules now.

* Add more tests

* Add a leak test

* Refactor exportables; Prepare for 'export use'

* Fix description

* Implement 'export use' command

This allows re-exporting module's commands and aliases from another
module.

* Add more tests; Fix import pattern list strings

The import pattern strings didn't trim the surrounding quotes.

* Add ignored test

crates/nu-protocol/src/module.rs

@@ -33,16 +33,16 @@ impl Module {
         }
     }
 
-    pub fn add_decl(&mut self, name: &[u8], decl_id: DeclId) -> Option<DeclId> {
-        self.decls.insert(name.to_vec(), decl_id)
+    pub fn add_decl(&mut self, name: Vec<u8>, decl_id: DeclId) -> Option<DeclId> {
+        self.decls.insert(name, decl_id)
     }
 
-    pub fn add_alias(&mut self, name: &[u8], alias_id: AliasId) -> Option<AliasId> {
-        self.aliases.insert(name.to_vec(), alias_id)
+    pub fn add_alias(&mut self, name: Vec<u8>, alias_id: AliasId) -> Option<AliasId> {
+        self.aliases.insert(name, alias_id)
     }
 
-    pub fn add_env_var(&mut self, name: &[u8], block_id: BlockId) -> Option<BlockId> {
-        self.env_vars.insert(name.to_vec(), block_id)
+    pub fn add_env_var(&mut self, name: Vec<u8>, block_id: BlockId) -> Option<BlockId> {
+        self.env_vars.insert(name, block_id)
     }
 
     pub fn extend(&mut self, other: &Module) {