nu-cli: directory syntax shape + completions (#5299)

crates/nu-command/src/filesystem/cd.rs

@@ -17,7 +17,7 @@ impl Command for Cd {
 
     fn signature(&self) -> nu_protocol::Signature {
         Signature::build("cd")
-            .optional("path", SyntaxShape::Filepath, "the path to change to")
+            .optional("path", SyntaxShape::Directory, "the path to change to")
             .category(Category::FileSystem)
     }
 

crates/nu-command/src/filesystem/mkdir.rs

@@ -21,7 +21,7 @@ impl Command for Mkdir {
         Signature::build("mkdir")
             .rest(
                 "rest",
-                SyntaxShape::Filepath,
+                SyntaxShape::Directory,
                 "the name(s) of the path(s) to create",
             )
             .switch("show-created-paths", "show the path(s) created.", Some('s'))